Preheat your oven to 375°F (190°C). In a large skillet, brown the ground beef for about 3–4 minutes until it's no longer pink. Add chopped yellow onion and sauté for an additional 3 minutes until translucent. Stir in minced garlic and crushed red pepper for 1 minute.

Pour in the marinara sauce, stirring to combine. Let this simmer on low heat for 5 minutes. Remove from heat and set aside.

In a large pot, bring salted water to a boil and cook lasagna noodles according to package instructions until al dente, about 8–10 minutes. Drain and cool in cold water.

In a mixing bowl, combine ricotta cheese, egg, grated Parmesan, 1.5 cups mozzarella, and chopped parsley. Stir until well-blended.

Spread a layer of cheese filling down the center of each lasagna noodle, top with a spoonful of meat sauce, and roll up tightly. Place seam-side down in a greased baking dish.

Gently pour the remaining marinara sauce over the roll ups and sprinkle with remaining mozzarella. Cover with foil and bake for 38 minutes, then remove foil and bake for an additional 2 minutes.

Let cool for a few minutes, garnish with parsley, and serve.