Bring a large pot of water to boil and cook the spaghetti according to the package. There are all different widths so I can't give you a time. Mine was 11 minutes. You can start the next step while the spaghetti is cooking, just drain and rinse with hot water (to rinse off some starch and keep it from clumping up while you're waiting.)
Brown the ground meat until no longer pink, then add the onion, green pepper and garlic and cook another few minutes until the vegetables are softened.
Stir the pasta sauce into the ground meat and vegetables. You can make your own marinara sauce or use a store-bought jar or can of sauce. If you have a bit more or less than 2 cups don't worry about and use it. If it seems to0 thick, add a bit of water. I usually do that just to rinse the jar out if I'm using store-bought sauce anyway.
Stir in the kidney beans. Cook 5-10 minutes to blend the flavors. Then stir in the cooked pasta.
Add about 3/4 of the cheeses and stir. You could of course do this with mozzarella but I'm only Italian by divorce and grew up with Cheddar in here and it tastes good to me. I don't claim the dish to be Italian! I am pretty sure my mother never put Parmesan in it but it seemed to add a nice touch to me. But skip if it you don't have it.
Pour this all into a 9x9 or similar casserole dish that can go in the oven. Top with the rest of the cheese. Bake at 350 for 30 minutes or so.