Directions

1. Gather all ingredients.
2. Bring a large pot of salted water to a boil. Add shells and cook, stirring occasionally, until tender yet firm to the bite, about 9 minutes. Drain well and set pasta aside.
3. Meanwhile, preheat the oven to 350 degrees F (180 degrees F). Lightly grease a 13- x 9-inch oven-safe baking dish with cooking spray; set aside.
4. Heat oil in a large nonstick skillet over medium-high. Add ground sirloin, 1/2 teaspoon salt, 1/2 teaspoon Italian seasoning, and 1/4 teaspoon pepper and cook, stirring occasionally, until beef is lightly browned but not fully cooked through, about 5 minutes. Add onion and 1 tablespoon garlic; cook, stirring occasionally, until onion is softened, about 5 minutes.
5. Reduce heat to medium; stir in marinara sauce, and cook, stirring occasionally, just until beginning to simmer, about 3 minutes. Remove from heat.
6. While beef mixture cooks, stir together ricotta, cream cheese, Parmesan cheese, basil, egg, remaining 1 1/2 teaspoons garlic, 3/4 teaspoon salt, 1/2 teaspoon Italian seasoning, and 1/4 teaspoon pepper in a large mixing bowl until evenly combined. Gently fold in cooked pasta until evenly coated.
7. Transfer 1/2 of the beef mixture (about 2 cups) into the prepared baking dish, spreading into an even layer. Top evenly with pasta mixture.
8. Spread remaining beef mixture over pasta layer, and sprinkle evenly with mozzarella cheese.
9. Cover baking dish loosely with aluminum foil. Bake in the preheated oven until bubbling around the edges and cheese is just beginning to melt, about 25 minutes. Uncover and continue to bake until cheese is fully melted and pasta is heated through, about 10 minutes more.
10. Remove from oven and serve, garnished with basil.