Heat oil in large skillet over medium heat until hot. Add onion, mushrooms, basil and fennel seed; cook 4 minutes or until onion is tender, stirring occasionally.
Stir in frozen vegetables. Place fish over vegetables; sprinkle with salt and pepper. Arrange tomato slices over fish. Reduce heat to low; cover and cook 12 to 16 minutes or until fish flakes easily with fork.
Sprinkle with cheese. Remove skillet from heat; cover and let stand about 3 minutes or until cheese is melted.