Sometime ago I read a recipe in one of the Moosewood cookbooks for what I think was called Mystery Marinara Sauce. You blend up some garden veggies and mix them into your regular spaghetti sauce.
This last weekend I had planned on spaghetti for dinner, but wanted to soup it up a bit. Usually, that would mean cooking up some Italian sausage, but Rob is still on the vegetarian kick so that wasn't an option. I remembered the Moosewood recipe and decided to wing it. I found a red pepper, yellow squash, and brocolli in the fridge. I sauteed them in olive oil, threw them in the blender (my Vita-Mix) with some Ragu, heated it up, and we had a delicious, yet healthy, spaghetti dish. I imagine you could do this with any leftover veggies. Give it a try.
Oh, one more thing. Mystery Marinara sounds too much like Mystery Meat to me, so I renamed it Spaghetti Sauce Surprise. I never did let onto the kids that I blended vegetables into the sauce and they were none the wiser!