Preheat oven to 350°F (175°C).

Brown hamburger and diced onion in a skillet over medium heat.

Drain excess grease from the skillet.

Stir in tomato sauce, tomato paste, sugar, salt, pepper, and garlic into the skillet with the browned hamburger and onion.

Simmer the meat sauce for 10 minutes.

Cook noodles according to package directions, then drain.

In a separate bowl, combine cottage cheese, cream cheese, sour cream, green pepper (if using), and green onions.

Spread half of the cooked noodles in the bottom of a baking dish.

Top the noodles with half of the meat mixture.

Spread the cheese mixture evenly over the meat layer.

Add the remaining noodles and top with the remaining meat mixture.

Sprinkle Mozzarella cheese evenly over the top.

Bake in the preheated oven for 30 minutes, or until bubbly and golden brown.