Here's an example of how you can turn a single vegetable and penne into a skillet pasta for any night of the week. The sauce is a combination of pasta water plus parmesan with an optional dab of butter and cream and is so easy.
Bring 4 quarts of water to a boil and add 1 tablespoon salt so that the pasta water is seasoned but will not make your finished skillet pasta over-salted.
Meanwhile, heat the oil in a large skillet over medium-high heat and when it shimmers, add the cauliflower, salt and pepper and stir together. Let the cauliflower cook undisturbed so that it browns. You'll hear it sizzling but resist turning it for at least 5 minutes. Stir once or twice until most of cauliflower is nicely browned, about 10 minutes total.
Cook the pasta until it is just tender to the bite since it will cook a bit more in the sauce. Reserve 1 cup of the pasta water and drain the pasta.
Add the onion, garlic and red chili flakes and cook until the onion becomes limp and the garlic is fragrant, about 2 minutes. Reduce the heat to low.
Add the pasta to the skillet along with about 1/2 cup of the reserved pasta water, the cream, if using, and parmesan. Stir well to coat the penne with this light sauce.
Taste the pasta for seasoning before serving, adding additional pasta water as necessary to keep it slick, and garnish with the parsley.