Preheat oven to 400 degrees. Line a baking sheet with foil. Add mahi-mahi fillets to baking sheet and sprinkle with salt and pepper. Bake for 15-20 minutes or until fish is opaque and flakes easily with a fork.
Add green beans to a microwave-safe bowl and cover with a damp paper towel. Microwave for 4-5 minutes until tender crisp. (Skip this step and microwave in the bag if you bought the green beans that steam in the bag.)
Combine mango, tomato, onion, lime juice, and cilantro. Add salt and pepper if desired. Mix and set aside.
Serve mahi-mahi over cooked quinoa and green beans. Top with mango salsa.