Heat 1/4 cup lard or vegetable oil in a large skillet over medium heat. Add 1/2 diced onion and cook, stirring, until soft, about 3 minutes. Add two 15-ounce cans black beans (drained), 1 cup chicken broth and 1/2 teaspoon dried Mexican oregano. Cook, lightly mashing the beans, until the liquid is absorbed, about 5 minutes. Add 1 more cup chicken broth and cook until slightly saucy, about 7 minutes. (Stir in a splash of water if the beans are too thick.) Season with salt and pepper and top with crumbled Cotija cheese.