Preheat oven to 425°. Slit each fillet down middle to create a long pocket in each (do not cut all the way through). Season fish with a pinch of salt and pepper. Combine pesto, green onions, capers, 1 T lemon juice and parsley. Stuff each fillet with approx.. 2 heaping T of filling. Top each with peppers and feta.
Place filets in ovenproof roasting pan or skillet, with tomatoes added around pan. Drizzle olive oil and butter over all. Bake until fish flakes in center, about 15 min. Garnish with basil and more parsley and capers, as desired.