Preheat an oven to 180 degrees C. Grease a 20x30cm baking dish.
Heat olive oil in a frypan over medium-high heat then add spring onions and mushrooms; cook and stir until tender, about 5 minutes. Season haddock with salt, pepper, garlic powder and chilli powder and place in the baking dish. Top with spring onion and mushroom mixture then dot with butter. Sprinkle parsley on top.
Cover with foil and bake in the preheated oven for 15 minutes. Remove foil and top haddock with cheese and return baking dish to the oven. Continue baking until the fish flakes easily with a fork and the cheese is melted, 15 to 20 minutes.