Preheat oven to 220 degrees Celsius. Lightly grease baking dish.
Drizzle potatoes and parsnips with 1 tbsp olive oil and spread evenly across baking dish. Bake for about 20 minutes until vegetables begin to soften.
Flip vegetables and continue to cook for a further ten minutes.
Place ocean trout on top of potatoes, add thyme sprigs and green onions, season with salt and pepper and bake for a further 8-10 minutes until ocean trout is cooked. Serve with lemon wedges on the side.