In a large skillet over medium heat, heat the oil. Add the onion. Add mushrooms, basil and fennel. Saute for 4 minutes or until onion is tender. Stir in frozen vegetables. Place fish fillets over vegetables, sprinkle with salt and pepper. Arrange tomato slices over fish. Reduce heat to low, cover and cook 12-16 minutes or until fish flakes with a fork. Remove from heat, sprinkle with parmesan cheese, cover and let stand until cheese melts (about 3 min).
