Cook manicotti in liberally salted water according to the directions.
Meanwhile, cook and crumble sausage in a large-skillet till sausage is cooked through & browned.
Add spinach then continue cooking for a couple of minutes or till spinach is wilted. Drain skillet if needed.
Remove sausage mix from heat and let it cool for 5 minutes. Then add 1 cup shredded mozzarella, ½ cup grated parmesan, garlic powder, egg, pepper and salt then blend well.
Spray a 13x9" baking-dish with cooking-spray (or rub with olive-oil). Spread ½ cup spaghetti-sauce at the bottom of the dish.
Drain manicotti nicely then stuff each tube with meat mix. Put stuffed manicotti in baking-dish.
Cover manicotti with sauce, cover tightly with aluminum foil and then bake at 375°F for 30-35 minutes or till sauce is tender.
Remove aluminum foil and top dish with remaining parmesan and mozzarella. Continue baking, uncovered for 20-25 minutes or till cheese is melted and lightly-golden.
Let dish rest for 15 minutes before serving. You can garnish with fresh chopped parsley if desired.