I love lasagna and, like Garfield, I've hardly ever met one I don't like, with the exception of a Montreal version full of dried chili peppers, and one that was supposed to be "vegetarian" and had these huge hunks of half-raw vegetables and whole spinach leaves spilling out of it.
I love making lasagna too, but I hardly ever stick to a recipe. It's so easy to improvise this (especially with oven-bake lasagna noodles) that I'm always trying to convert people who tell me "I want to make lasagna but it's too expensive" or "my recipe calls for ground pork or something else I don't have or can't afford."
In the last twenty years or so I've made shrimp lasagna, overnight brunch lasagna [Update: our version], white mushroom lasagna, tofu lasagna, tofu-with-no-cheese lasagna (a very interesting Vegetarian Times recipe), chard lasagna (chard from our garden), and "regular" ground-beef lasagna. And we've made lasagna roll-ups, and stuffed shells which are almost the same thing. About six years ago I wrote an article for an online newsletter called "Iron Chef Lasagna." (I know when it was because I remember mashing some of it up for baby Crayons.) And tonight I made leftover-sausage lasagna.
So I can't give you a recipe but I can try listing some pointers; then you can use "what you have in your hand."
1. For a lasagna that serves about 4 to 6 people, you will need about 4 cups of canned pasta sauce; that's a 680 ml can plus a little bit. I pour the can of sauce into a 4-cup measure and then top it up with water. If you're using pre-cooked noodles (that is, you've cooked them soft in a pot of boiling water before using them), you might not need as much sauce. By the way, you can experiment by using regular lasagna noodles as oven-bake ones; whole wheat noodles (even if they don't say oven-bake) will usually cook just fine even if you don't pre-cook them. Saves a pot and a bit of time; just make sure you have enough sauce in the casserole to cook them well.
2. You will also need some version of a cottage-cheese/ricotta-cheese/tofu filling layer, which can incorporate fresh or frozen spinach or chard. (If I'm using fresh spinach or chard, I steam it and then drain (squish) it dry before chopping it into the filling.) I usually beat an egg into it and add some seasonings like salt, garlic powder or nutmeg (good with spinach). If it's too wet, add breadcrumbs. I often make this filling in the food processor, processing some dry bread first and then adding the rest. Tonight I had some leftover frozen chopped spinach (not cooked) and I just stirred that into some cottage cheese/egg/breadcrumbs, making sure it had enough crumbs in it to allow for extra moisture coming from the spinach.
3. You will probably want some grated cheese; mozzarella is good, of course, but you can use other kinds too. The amount is up to you; I've had some restaurant lasagna that seemed to be half cheese, but most home versions don't need that much.
4. And you can incorporate ground meat (browned), cooked sausage, canned shrimp, pepperoni, or other things like zucchini and mushrooms (just make sure they're going to get cooked and that they're cut small enough that nobody ends up with a huge hunk of vegetable). Add the meat to the sauce if you want, but I like making a separate layer of it. You can add in anything else you want too, like a layer of sliced tomatoes.
5. Try using a big lidded casserole instead of an open lasagna pan; you can take the lid off near the end if you want. Covering the casserole works especially well with oven-bake noodles, and the oven doesn't get as spattered. You can always put the casserole on a cookie sheet too.
6. Start and end your layers with sauce; otherwise the order is pretty much up to you. Something like this: sauce, noodles, stuffing, noodles, sauce, meat layer, cheese, noodles, sauce. Three or four layers of noodles are fine. You'll probably have to break them shorter if you're using a casserole instead of a flat lasagna pan. Leave lots of room between noodles so they can expand. And make sure there's enough sauce on top (even if you have to open another can of sauce), because otherwise you'll get that yucky dried-out layer of noodles on top.
7. Don't put cheese right on the top, it gets tough. Under the top layer of noodles is usually a good place for a layer of melted cheese. I like to sprinkle the whole thing with Parmesan when it comes out.
8. Bake the whole thing for about an hour at 350 degrees. Check the noodles gently with a fork to see if they're as soft as you want.
9. Let it sit about 10 minutes before you try to cut it. Leftover lasagna always cuts better (and tastes better the next day too, if you can reheat it without drying it out).
And that's it!