I love baked spaghetti. It's such a comfort food. I've created a version that I love, and will share it here. It's not so much a recipe - I just go by feel, so you can tinker with it at will.
2 cloves garlic, chopped
1 onion, chopped
1 green pepper, chopped
2 carrots, sliced
4 ounces sliced fresh mushrooms
Mild Italian Sausage
1 box spaghetti
1 jar spaghetti sauce
Preheat oven to 375*. Heat olive oil in skillet. Add onions and garlic, sauté until tender. Add sausage (casings removed, if you buy that type). Meanwhile, start boiling spaghetti and cook according to instructions on box. Once sausage is partially browned, add green peppers and carrots. Continue to sauté until softened. Add mushrooms.
Drain spaghetti and return to pot, toss with jar of spaghetti sauce. Layer half in 9 x 13 pan. Put half the veggie/sausage mixture on top. Sprinkle cheeses (about 1/2 cup of each). Layer again - spaghetti, veggies, cheeses. Cover with aluminum foil (try to tent it, so that it doesn't touch the cheese on top) and bake for 30 minutes.