In a large ovenproof skillet, brown Italian sausage over medium/high heat until its cooked through, about 5 minutes. Remove the pan from heat.
Add the marinara sauce, ricotta, uncooked gnocchi, fennel seed and salt to the pan with the cooked sausage, and stir gently until the gnocchi is coated with the sauce and the sausage is well-distributed. Top with mozzarella and bake on center rack for 30 minutes (or until gnocchi is tender).
Top finished baked gnocchi with a sprinkling of fresh parsley and serve warm.