Preheat oven or toaster oven to 350°F. Wrap tortillas in aluminum foil and heat in oven until warm, about 10 minutes. Set aside and keep warm.
In a bowl, whisk lime juice, olive oil and cumin together and season with salt and pepper to taste. Add black beans and gently toss in vinaigrette. Add mango, cilantro, green onion and chili and toss again or gently mix with a rubber spatula.
To serve, spread about 3 tablespoons of mango mixture on the centre of each warm tortilla. Top with 1/4-cup chicken and garnish with sour cream and cheddar, if desired. Fold bottom of tortilla over filling and roll from the sides.
Nutrients per serving (based on 4 servings): 780 calories, 34 g fat, 37 g protein, 11 g fiber, 77 g carbohydrates. Excellent source of vitamin A, vitamin E, niacin, vitamin B12, calcium, iron. Good source of vitamin C, riboflavin, vitamin B6, zinc.