Heat vegetable oil in a medium, non-stick skillet over medium heat. When oil is hot, add onion, garlic and chilis; saut‚ until onions are soft, about 5 minutes. Add the beans and cook, smashing down on them with the back of a large spoon, until softened and heated through, another 2-3 minutes. Add Oaxaca cheese, sour cream, cumin and cayenne and cook until cheese is melted. Add salt and pepper to taste. Transfer to a serving dish and sprinkle Cotija cheese on top. Serve warm with chips and vegetables.
Per serving: 80 calories, 4g protein, 10mg cholesterol, 100mg sodium, 1g fiber, 5g fat (2.5g saturated fat), 62% calories from fat, 4g carbohydrates