Heat 1 tbsp oil in a skillet over medium heat. Add the onion and cook 3 to 4 minutes until soft. Add the garlic and cook 30 seconds.

Stir in the black beans, cumin, chili powder, and salt. Cook 2 to 3 minutes, lightly smashing some of the beans. Add a tablespoon of water if the mixture looks dry.

Wipe the skillet clean, return it to medium-high heat, and brush with oil. Sprinkle half the cheese over one tortilla, spoon half the beans onto one half, fold it over, and press down. Repeat with the second tortilla.

Cook both quesadillas for about 2 minutes per side until golden and crisp. Cover the pan for the last 30 seconds if the cheese needs help melting. Let rest 1 minute, slice, and serve.