Place green beans into a colander, set aside to drain.
Spray skillet with non stick spray, saute chopped onion until translucent (about 5 minutes) And hamburger and cook until browned.
Stir in spaghetti sauce, simmer five minutes, uncovered.
While meat is simmering, take paper towels and press the excess water out of the green beans. Get the green beans as dry as possible. (Divide into 3 portions)
Spray an 11x13 baking dish with non stick spray.
Layer 1/3 of the green beans into the casserole dish.
Layer 1/3 of the meat sauce.
Layer 1/3 of the mozzarella cheese.
Repeat layers two more times, finishing off with the mozzarella cheese.
Top with a generous sprinkle of Parmesan cheese.
Bake 30 minutes until lightly brown and bubbly.
Remove from oven and let rest for five minutes before serving.
OPTIONS: You can use taco meat filling instead of spaghetti sauce mixture and cheddar instead of the mozzarella for an enchilada casserole.
You can use diced or shredded chicken and Alfredo sauce instead of the spaghetti sauce. (using Alfredo sauce will usually lower the carbs considerably)