Take knife and poke about 6 holes in the top of a spaghetti squash - sit on baking pan in oven for about 1 hour and 15 minutes on 325-350 - some say they use the microwave, but i would be afraid it might blow up - when done allow to cool until you can handle it - cut open, not long ways - scoop out innards - take fork and in a circular motion, pull out the spaghetti like strands.
Place in bowl, and mix in some spaghetti sauce. Toss into baking pan. Add layers of your choice such as low fat cottage cheese, lean browned hamburger, diced onions, minced garlic, diced green peppers, sliced mushrooms, parmesan cheese, mozzarella cheese. Bake at 350 for about 1 - 1/2 hours.
If casserole seems watery, its from the squash. Mine did, and I just tilted the dish over GENTLY LIKE and poured off the water - then i baked it a lil longer - .