In a square glass dish layer small amounts of marinara, fish, ricotta, cheese and a layer of sauce.
Repeat, finishing with a layer of mozzarella cheese.
Bake covered at 350 degrees F. for 40-50 minutes, then bake uncovered another 10 minutes.
Sprinkle with parsley.
If you have a favorite commercial marinara...use it. If you like to make your own - go ahead. How much sauce and ricotta you need will be determined by how wet and how ricotta-rich you like it. I'm a heavy-sauce, light-cheese gal, myself.