Preheat oven to 350F.
Boil manicotti 4-6 minutes until al dente. Allow to cool on an oiled or silicone mat lined baking sheet. Prepare desired filling and fill each manicotti shell with cool filling.
Spread 1 c. marinara sauce onto 9×13 inch glass baking dish and place filled manicotti in a single layer in the dish. Pour remaining sauce on manicotti layer.
Top with mozzarella and parmesan and bake for 30-40 minutes.
Let rest for 5 minutes out of the oven and serve!
Ground Beef Filling
Heat a skillet with 1 tsp of olive oil over medium heat and once hot, add onion and ground beef.
Season with soy sauce and ground pepper to taste. Sauté until the beef is brown and the onion is soft and translucent, let sit to cool.
Boil manicotti for 4-6 minutes until they are slightly soft, but still firm.
Transfer manicotti to an oiled baking sheet or one with a silicone baking mat and allow to cool.
Combine ricotta, 1 ½ c. mozzarella cheese, ½ c. parmesan, parsley, garlic, salt and pepper in a bowl. Add the cooled meat mixture to cheese mixture and combine gently.
Spinach and Ricotta Filling
Fold all ingredients together.