Preheat the oven to 425 degrees Fahrenheit.
In a bowl, combine the black beans, garlic, cilantro, cumin, salt and lime juice. Using a potato masher or the back of the spoon, mash everything together until it is combined, smooth with some chunks of black bean.
Place a heaping tablespoon of the black bean mixture on one side of the tortilla, sprinkle it with cheese and roll it up. Place the taco on a parchment lined baking sheet (or a buttered baking sheet) with the open edge facing down, folded under. Repeat with the other tortillas.
Brush with butter and bake in the oven about 10-15 minutes or until warmed and crispy. Serve with a dollop of sour cream and enjoy!