Preheat the oven to 350°F (180°C). Heat the olive oil in a large frying pan over medium-high heat. Add the Italian sausage meat, breaking up any lumps with a wooden spoon, and cook until browned and cooked through. If necessary, drain excess fat (about 2 tablespoons is fine).
Pour in the marinara sauce, stirring to combine, and allow to simmer until heated through. Remove from heat.
Spread one-third of the sausage and marinara mixture evenly across the base of a 9 x 13-inch baking dish. Layer half of the ravioli over the sauce, followed by half of the mozzarella and a light sprinkling of Parmesan. Add a few basil leaves between the ravioli for added flavor.
Repeat the layers: Spread another one-third of the sausage mixture, add the remaining ravioli, and sprinkle half of the remaining Parmesan cheese and some basil leaves.
Top with the last one-third of the sauce mixture, then finish with the remaining mozzarella and a generous sprinkling of the Parmesan cheese.
Place the dish in the preheated oven and bake for 20 to 30 minutes, or until the sauce is bubbling and the cheese is golden and melted.
Remove from the oven, sprinkle the chopped basil over the top, and serve.
