Heat oven to 425.
In a medium saucepan, saute chopped onion in oil, till limp and add garlic and saute one more minute.
Add tomatoes and salt and Italian seasoning.
Bring to a boil, stirring occasionally.
Spray 2 quart casserole with cooking spray.
Make two layers dividing ingredients evenly in this order: Tomato mixture, chopped basil, shrimp, feta, and Parmesan, and repeat.
Sprinkle with a small amount of extra Italian seasoning and garnish with extra basil leaves, if desired.
Bake 15-20 minutes or until cheese is just melted. Do not over bake. Serve immediately.