Place each salmon fillet on top of a piece of aluminum foil. Top each fillet with about 2 tablespoons pesto, ¼ cup of onion, ¼ of the tomatoes, and approximately 2 tablespoons of feta cheese. There's no need to measure the ingredients -- just use as much or as little as you like!
4 salmon fillets, 1/2 cup prepared pesto, 1 onion, 1 pint grape tomatoes, ½ cup crumbled feta cheese