2. To make the citrus relish, combine the grapefruit and orange sections in a mixing bowl. Add the lemon juice and tarragon and set aside. (This can be made in advance and stored in the refrigerator for up a day or two. The relish should be served at room temperature.)
3. Brush the fillets with oil and season generously with salt and pepper. Place the seasoned fillets on a non-stick baking sheet.
4. Broil the fillets for 3 to 4 minutes on each side, turning only once. (Thin fillets will take less time, thicker fillets will take more.)
5. Place the fillets on warmed plates, top with citrus relish and serve immediately.