Preheat oven to 350 degrees. Spray a 9x13 baking dish with nonstick spray. Set aside.
Heat oil in a large skillet oven medium heat. Add diced onion and cook until slightly softened, about 3-4 minutes. Add ground beef, salt, and pepper, Break down the beef so it's crumbled. Cook until it's browned, about 5 minutes. Remove from heat and drain beef and onions to remove excess fat.
Add jar of tomato sauce to beef in the skillet. Heat over medium until sauce is warmed. Spread ½ of sauce on the bottle of the baking dish. Layer half of the frozen ravioli over the sauce. Next, layer on half of each cheese and then sprinkle with half of the Italian seasoning.
Next, repeat with the rest of the ravioli and then top with the rest of the meat sauce. Top with the remaining cheese and Italian seasoning. Bake in preheated oven for 40 minutes or until all the cheese has melted, is bubbling, and slightly browned around the edges of the baking dish.
Remove from oven and let it cool for a few minutes before servings.