Cook spaghetti until al dente, 8-9 minutes, then drain and rinse under cold water.
3
In a large bowl, whisk 3 eggs. Add the cooled spaghetti, 1 1/2 cups shredded mozzarella, 1/2 cup grated Parmesan, and 1 cup marinara. Toss to combine.
4
Spray a muffin tin with cooking spray and press the spaghetti mixture into each cup, creating a well in the center.
5
Bake the spaghetti cups for 15 minutes or until they're set.
6
While the spaghetti cups are baking, heat the store-bought meatballs in a large skillet with the remaining 2 cups marinara, simmering for 5 minutes.
7
Season the meatball sauce with 1 teaspoon kosher salt and 1/2 teaspoon freshly ground black pepper.
8
Place one meatball in each spaghetti cup, pour a spoonful of marinara sauce on top, and garnish with chopped parsley and the remaining 1/4 cup grated Parmesan.