Preheat oven to 425 degrees. Lightly grease a baking sheet.
Place cubed sweet potatoes in a resealable plastic bag. Dust with 1 tsp cumin, and chili powder. Pour in 1 tablespoon olive oil and seal the bag. Give the bag some good shaking so that all of the sweet potato cubes get coated with spices. Spread sweet potatoes out on the prepared baking sheet and cook in the preheated oven for about 30 minutes, until sweet potatoes are soft. Keep the oven on.
Meanwhile, in a skillet over medium-high heat, saute the onion in the remaining 1 tablespoon olive oil for about 5 minutes, until soft. Add in the minced garlic, chipotle peppers, and remaining 1 teaspoon cumin and saute for about another minute to release the flavors. Remove from heat and stir in the black beans and set aside.
Assemble your burritos by first putting on a scoop of sweet potatoes down the center, then a nice helping of the beans, some avocado, then a fistful of cheese. Fold burrito style. Place the assembled burritos on another baking sheet.
Bake in the preheated oven for about 10 to 15 minutes, until cheese is melted. Serve hot with sour cream or guacamole.