Preheat oven to 350 degrees F. Season the shrimp with salt and pepper. Place the shrimp into a casserole dish in one layer. 

In a medium bowl, combine the onion, garlic, Basil and Parmesan.  Stir to combine well.  Evenly spread the mixture over the shrimp. Bake for 9-11 minutes or until the shrimp are cooked through and no longer opaque. Serve warm garnished with fresh basil leaves.

Store in an airtight container in the refrigerator for up to 4 days. To reheat, place in a casserole dish in a 350 degrees F oven for about 3 minutes, until heated through.