Preheat your oven to 375°F (190°C). In a medium skillet, add a drizzle of olive oil over medium heat. Once hot, brown the ground beef, breaking it apart with a spatula until no longer pink, about 5-7 minutes. Add diced onion and minced garlic; sauté until onion turns translucent, about 3 minutes.

Stir in marinara sauce into the beef mixture, ensuring well combined. Allow to simmer gently for about 5 minutes.

Prepare the cheese-filled ravioli according to package instructions, usually boiling them in salted water for about 4-6 minutes until al dente. Drain well and set aside.

In a greased casserole dish, start layering by spooning half of the beef mixture across the bottom. Next, add a layer of the cooked ravioli, followed by a sprinkle of shredded mozzarella cheese. Repeat with remaining beef, ravioli, and finish with mozzarella and Parmesan.

Cover tightly with aluminum foil. Bake for 20 minutes. Remove foil and bake uncovered for an additional 10 minutes until cheese is bubbly and golden.

Let cool for about 5 minutes. Garnish with fresh basil leaves before serving.