Preheat the oven to 350 degrees F. Grease two 9-inch x 13-inch baking dish. Set aside.
Heat 3 teaspoons vegetable oil in a large skillet over medium heat. Add 1 cup yellow onion and cook for 5 minutes or until tender. Add 1 pound sweet potatoes and 1 1/2 cups water to the skillet and bring to a boil. Cover and cook for 5-8 minutes or until the potatoes are fork-tender.*
Push the potatoes to the sides of the pan, add the remaining 1 teaspoons vegetable oil and 3 cloves garlic. Cook for 30 seconds until fragrant. Mix in 2 teaspoons chili powder, 3/4 teaspoon salt, 1/2 teaspoon ground cumin, 1/4 teaspoon black pepper, 1/4 teaspoon cayenne pepper, 15 ounces canned black beans, 1 cup fire-roasted corn, and 1 ounces red enchilada sauce (2 tablespoons). Cook for 1-2 minutes until heated through.
To Assemble: Place 2 tablespoons of cheese down the middle of a tortilla** and then top with ⅓ cup of the sweet potato filling. Roll up from one side to the other and place seam side down in the prepared baking dish. Repeat with remaining ingredients. (I can usually fit 7 enchiladas per dish.)
Pour the remaining 9 ounces red enchilada sauce all over the top of the tortillas. Top with the remaining 1 ¼ cups of cheese. Bake for 15 minutes or until the cheese is melted.
Remove from the oven and let rest for 5 minutes. Top with 1 cup cherry tomatoes, 1 avocado, and 1/4 cup cilantro. Serve immediately.
Notes
*Drain any excess water from the sweet potato filling before adding the beans, corn, and spices.**Warm the tortillas before rolling so they are easier to fill and less likely to tear.
For gluten-free enchiladas, use corn tortillas and a gluten-free enchilada sauce.
If using cold make-ahead filling, add 5 to 10 extra minutes to the bake time.
Store leftovers covered in the refrigerator for up to 3 days.
Reheat covered in a 350°F oven for about 20 minutes, or until warmed through and bubbly around the edges. Microwave individual portions for 1 to 2 minutes, adding more time as needed.