Homeschooling plus lunch can be kind of an odd combination/situation, especially if you're in the kind of family where hot food is called for at noon, and if you're both the Teacher and the Cafeteria Lady. You don't always want to be eating peanut butter and canned soup.
There are lots of things you can put together quickly, though. Or at least within half an hour. Here's one version of leftover soup that I started after Just-So Stories this morning (that was at about 11:30, and we ate at just after 12.) It's not a recipe, just what I did. Amounts are approximate.
Sausage-Barley Soup (Like Grandma's)
In a large pot, combine about four cupfuls of water and about half a cupful of (rinsed) small red lentils (because they cook the fastest). Bring to a boil and boil hard for a few minutes.
Stir in half an envelope of onion soup mix (why I had half an envelope of onion soup mix), a cooked, sliced leftover Polish sausage along with a cupful or more of the barley we cooked with the sausage, and two stalks of celery, sliced thinly. Cook it all as hot as you can without burning it or letting it boil over (i.e. on medium) until the lentils are all cooked and the barley has slightly thickened the broth (i.e. 20 minutes to half an hour). (If you're not in a hurry, you can just turn it down to a nice simmer and go do something else.)
Mr. Fixit: "It tastes like Grandma's."
Mama Squirrel (joking): "Grandma used onion soup mix?"
Mr. Fixit: "Yep."
Variations for a slower morning or fewer leftovers: use raw barley or rice, or bigger lentils, or split peas, or beans, and just cook the whole thing longer (even in the crockpot). Start with chopped onion as well as celery, and maybe start the whole thing by sauteeing the vegetables in margarine or olive oil. Add some leftover tomatoes or tomato sauce (gives it a different flavour). Use another kind of soup base (chicken is good with sausage and barley), or real chicken or vegetable stock. A small amount of mashed squash or sweet potato always goes well with sausage and barley too.
And then you can get back to school.