Step 1 Preheat oven to 160°C. Heat olive oil in a large flameproof casserole dish (which has a lid) set over medium heat on the stovetop. Add onion and fennel to dish; stir for 5 minutes, or until soft. Add garlic and chilli flakes; cook, stirring, for 1 minute, or until mixture is fragrant.
Step 2 Add butter beans and cherry tomatoes to casserole dish with 1/3 cup water; bring to the boil, then simmer for 5 minutes, or until sauce thickens. Add prawns and fish to dish. Cover dish with lid and transfer to oven; bake for 10–15 minutes, or until seafood is cooked through.
Step 3 Remove casserole dish from oven and season baked seafood with cracked black pepper.
Step 4 Divide baked seafood among 4 bowls, scatter with crumbled feta and chopped parsley, and serve with steamed greens.