Rinse 1 cup of quinoa under cold water to remove its natural coating, then drain well.
In a medium saucepan, combine the rinsed quinoa with 2 cups of water or vegetable broth. Bring to a boil over medium-high heat, then reduce heat to low, cover, and simmer for about 15 minutes until tender and liquid is absorbed.
Fluff the cooked quinoa with a fork and set aside to cool.
Dice the ripe mango and red bell pepper into bite-sized pieces. Finely chop the red onion and roughly chop the fresh cilantro.
If using frozen corn, thaw by rinsing under warm water or microwaving briefly; if fresh, steam or boil until tender.
In a large mixing bowl, combine the cooled quinoa, black beans, diced mango, red bell pepper, corn, red onion, and cilantro. Toss gently to combine.
In a small bowl, whisk together the lime juice and olive oil. Season with salt and pepper to taste.
Pour the dressing over the salad and toss until everything is well coated.
Refrigerate the salad for at least 30 minutes before serving to allow flavors to meld.
Serve chilled or at room temperature.