1medium-sized tomatocored and finely chopped (no need to discard the seeds)
Heat the oil in a medium-size saucepan over medium-high heat. Once the oil appears to shimmer, add the onion and garlic and stir-fry until the edges are light brown and the raw smell dissipates, 3 to 5 minutes.
Stir in the cumin and salt. The heat of the pan’s contents is just right to cook the spice without burning it, about 10 seconds. Add the black beans, cream cheese, and chile and cook, stirring occasionally, to soften the cheese, 3 to 5 minutes.
Stir in 1 cup water. The result will appear curdled and slightly unruly. The water will quickly come to a boil. Cook the queso, stirring occasionally, until the sauce appears smooth and curdle-free, 3 to 5 minutes.
Stir in the shredded cheese, cilantro, and tomato. As soon as the cheese melts, remove from the heat and serve.