Heat the olive oil in a skillet over medium heat. Add the diced onion and cook until it softens. Stir in the minced garlic and cook for one minute more.

Add the black beans, cumin, chili powder, and salt to the skillet. Mash some of the beans with a spoon while stirring so the mixture holds together. Remove from heat.

Spread a thin layer of enchilada sauce in the bottom of a 9x13 baking dish. Spoon the bean filling into each tortilla, add a sprinkle of cheese, roll tightly, and place seam side down in the dish.

Pour the remaining enchilada sauce over the rolled tortillas and scatter the rest of the cheese on top. Bake at 375°F for 20 minutes until the cheese melts and bubbles.

Let the enchiladas rest for five minutes after baking. Place the sour cream in a zip-top bag, snip off one corner, and pipe four or five concentric circles across the top. Drag a knife through the circles in straight lines to form the web. Add olive slices if using.