Rinse the quinoa in a strainer several times with cold water. In a medium pot over medium-high heat, add 1 1/4 cups water and bring to a boil. Add the quinoa, cover, and turn off the heat. Allow the quinoa to steam until the water has been absorbed completely and the quinoa grains pop open, 10 to 15 minutes. Fluff with a fork. Set aside to cool.
In a large mixing bowl, add the vinegar, mustard, garlic, shallot, 2 teaspoons salt and 5 to 6 turns freshly ground black pepper. While pouring in a slow, steady stream, whisk in the olive oil until fully incorporated and lightly emulsified. Add the peppers, mango, mint and quinoa. Toss to combine well and serve.