Heat the oil in a medium saucepan over medium-high heat. Add the onion and jalapeno to the pan and cook, stirring occasionally, until tender, 3-5 minutes. Reduce the heat to medium-low. Add both the cheeses and ¼ cup of the milk. Whisk or stir until completely melted. Stir in the tomato and cilantro. Add additional milk gradually as necessary to achieve desired consistency. Serve immediately.