Preheat the oven to 375°F. Bring a large pot of salted water to a boil. Add pasta and cook al dente according to package instructions. Drain, reserve ½ cup pasta water, and transfer the pasta to a 9x13 baking dish.

In a large deep skillet over medium-high, heat the olive oil. Add the ground beef and onions and season with Italian seasoning, salt and pepper. Cook the ground beef and onions, breaking up the beef into smaller pieces with the back of a wooden spoon until browned, about 10 minutes.

Add the garlic and cook until fragrant, 1 more minute. Stir in the marinara and basil, then transfer the sauce on top of the pasta in the baking dish and toss gently to combine. Add as much of the reserved pasta water as desired until the sauce looks glossy.

Sprinkle the shredded mozzarella cheese on top and bake in the preheated oven until the cheese is lightly golden, about 15 minutes. Garnish with fresh basil and serve immediately.