Place into a bowl with the mint and half of the fennel tops. Add the orange slices and lemon juice and stir to combine. Drizzle in one tablespoon of the olive oil and season, to taste, with salt ...
Preheat the oven to 200C/400F/Gas 6 (180 fan). Butter the serving dish. Trim the tops from the fennel and cut each bulb in half through the root, then cut each half lengthways into three wedges.