In a bowl, toss together sweet potato cubes, olive oil, chili powder and salt. Transfer onto a baking sheet. Roast for 10-15 minutes or until tender and slightly golden.
In a small saucepan add black beans, water, garlic and cumin. Simmer until water is reduced by half. Remove from heat and smash into a paste using a potato masher.
Meanwhile, lightly brush tortillas with olive oil. Place on a cookie sheet and bake in 450 degree oven for 10 minutes or until crispy, flipping once.
Top crispy tortillas with a heaping tablespoon of smashed black beans and cheese. Return to oven for a few minutes, or until cheese is melted. Remove from oven and add roasted sweet potatoes, salsa, avocado and scallions.