Preheat oven to 350 degrees.
Chop up one small onion.
Cook ground beef and onion over medium.
Boil water and cook manicotti according to package instructions. Adding a tsp of oil and a pinch if salt helps to keep the noodles from sticking.
Add 26 oz of tomato sauce to cooked ground beef.
Pour half of the sauce mixture in the bottom if a casserole pan (9x13-ish pan).
Drain the noodles and rinse with cold water so you won't burn your hands when stuffing them.
Stuff each noodle with a string cheese and place in the pan.
Pour the remaining sauce mixture on top of the stuffed noodles.
Spread the sauce evenly over the top if the noodles.
Cover with foil and bake for 25 minutes.
Remove foil and sprinkle 2 cups of shredded mozzarella cheese on top. Leave uncovered and bake for about 5 more minutes.
Once the cheese is melted remove from the oven.
Serve and enjoy.