Preheat the oven to 350°F. Coat a 9 x 13" baking dish with nonstick cooking spray.
In a large skillet on the stove, over medium-high heat, add ground beef and onions. Cook, stirring frequently until ground beef is browned and onions have softened and are slightly translucent, about 10 minutes. Drain liquids and return skillet to stovetop. Stir in minced garlic and marinara sauce, and simmer for 5 minutes.
Meanwhile, in a mixing bowl, add ricotta, egg, 1/4 cup parmesan, basil leaves, garlic powder, and salt and pepper. Stir until well combined.
Spread 1/3 of the meat sauce across the baking dish. Top with a layer of ravioli, another 1/3 of the meat sauce, half of the ricotta mixture, half of the mozzarella cheese, and the remaining parmesan. Repeat layers again, with the final top layer being the rest of the mozzarella cheese.
Cover pan loosely with aluminum foil and bake for 30 minutes. Remove aluminum foil and bake for another 15 minutes, or until the cheese on top is bubbly and starting to brown.