Mix tomatoes, onions, cilantro, Serrano chiles, extra-virgin olive oil, lime juice and avocadoes together in a large bowl. Season with salt and freshly ground pepper to taste. Let the flavors come together at room temperature for about 1 hour. Coat fish fillets with olive oil, salt and fresh pepper and sauté about 4 minutes per side. To serve: Place fish on a platter and top with salsa. Serve with green salad and rice.