In the slow cooker, combine the frozen meatballs and marinara sauce. Stir to coat the meatballs evenly with the sauce.
In a separate bowl, mix together the ricotta cheese, Italian seasoning, garlic powder, salt, and black pepper until well combined.
Layer half of the cooked pasta over the meatballs in the slow cooker. Spoon half of the ricotta mixture over the pasta, followed by half of the mozzarella cheese.
Repeat the layers with the remaining pasta, ricotta mixture, and mozzarella cheese.
Cover the slow cooker and cook on low for 4-6 hours or on high for 2-3 hours, until the meatballs are heated through and the cheese is melted and bubbly.
Before serving, sprinkle the grated Parmesan cheese on top and let it sit for 5 minutes. Garnish with fresh basil leaves if desired.