Fennel and citrus are a natural pair, and together with creamy avocado and oil-packed tuna fish, they make a vibrant and delicious salad.
Cut fennel bulbs into 1-inch wedges. On a rimmed baking sheet, drizzle fennel with 2 tablespoons olive oil and sprinkle with salt. Roast at 400 degrees until golden, 30 minutes, flipping halfway through. Arrange on a platter with watercress, avocado, sliced oranges, and tuna. Juice 1/2 an orange and whisk in an equal amount of vinegar; whisk in olive oil and season. Drizzle over salad.