Preheat oven to 450 degrees. Spray a nonreactive pan with non-stick cooking spray. Add fish filets and sprinkle with salt and pepper.
Melt butter over medium heat. Add onions, mushrooms, zucchini, tarragon, and salt and pepper to taste; sautee for five to seven minutes or until vegetables are tender.
Top fish with mushroom-zucchini mixture and sprinkle with paprika. Bake, covered, for twelve to twenty minutes, depending on thickness of filets. Fish will flake easily with a fork when cooked through.