Preheat the oven to 400℉.
In a bowl, combine diced sweet potatoes, olive oil and chipotle chilis in adobo sauce. Toss to combine.
Roast sweet potatoes on a baking sheet for 20-25 minutes, until tender when pierced with a fork.
While potatoes are roasting, heat olive oil in a large skillet on medium heat. Add onions and saute 5-7 minutes or until translucent. Add garlic and continue cooking for 30 seconds to 1 minute. Add black beans and continue to cook, stirring occasionally for 10-15 minutes until the beans are soft and heated throughout. If the beans seem dry, add a few tablespoons of water. Season with salt and pepper.
Wrap tortillas in foil and place directly on the oven rack. Heat for 5-7 minutes until heated through.
While the tortillas are heating, make the lime crema. Combine the sour cream, lime juice and zest in a small bowl. Stir to combine. Season with salt and pepper.
Fill tacos with seasoned beans and sweet potatoes. Top with lime creme, diced avocado, cotija cheese and fresh cilantro.
