Season the fish with salt and pepper. Spread the pesto on top of each fillet. Cut two pieces of parchment paper and place one filet in the middle of each. Top with tomato slices and fold the parchment to create a sealed packet. (Alternatively, you can bake this in a covered dish, though you will likely need to add another 5 minutes to the cooking time.)
Bake at 400ºF for 15 minutes, or until the fish flakes easily when tested with a fork.