Prepare water to boil and pre-grease a deep casserole dish.
Brown beef, onions and garlic in a medium sized sauce pan (if you don't like your onions a tad crisp, saute your onions and garlic until soft, prior to adding the beef).
Add spaghetti sauce AND spinach to the beef, onion and garlic; cover and simmer for 15 minutes.
Pre-heat oven to 350, and add noodles to boiling water and cook until al dante.
Drain noodles and return to pot.
Pour the sauce mixture into the noodles, RESERVING two or so cups, and mix thoroughly. Set remaining sauce aside.
Pour half of the pasta mixture into the pre-greased casserole dish, layer with 6 slices of provolone cheese, pour in the remaining pasta, break the remaining provolone into pieces, layer, and sprinkle mozzarella cheese on top. Finally, pour on the reserved sauce.
Bake, covered, on 350 for 35 minutes.
Uncover, sprinkle parmesan cheese on top, and bake for an additional 5 minutes.