1. Preheat oven to 375 degrees F.
2. Coat salmon fillets with oil on both sides and season with 1⁄4 teaspoon salt and 1⁄4 teaspoon pepper. Place fillets skin-side down on aluminum foil-covered baking sheet and bake in oven for about 20 minutes until cooked through (internal temperature should be about 145 degrees F).
3. While salmon is baking, in a separate bowl, mix together grapefruit segments, orange segments, lemon and lime juices, mint, 1⁄4 teaspoon salt, and 1⁄4 teaspoon pepper. Let fruit salad sit and marinate while salmon finishes cooking in the oven.
4. Once salmon is cooked through, remove from oven and let rest for 5 minutes. Add avocado to citrus salad just before serving alongside salmon.