Heat a cast-iron skillet (or oven-safe skillet) over high heat. Once hot, add the vegetable oil. Add the cooked chorizo, onion, bell peppers, cilantro, jalapeno, and chili powder. Sauté until soft, about 2-3 minutes, stirring often. Remove from the heat.
Turn on the oven broiler to high heat.
Sprinkle the shredded cheeses evenly over the chorizo and vegetable mixture. Do not attempt to stir the ingredients, as they will get clumpy.
Place the skillet under the broiler for 3-4 minutes, or until the cheese is melted, browned, and bubbling.
Carefully remove the skillet from the oven. Top the queso fundido with the juice of 1 lime, some diced tomatoes, and more cilantro, if desired. Serve warm with tortilla chips.
Notes
To cook ground Mexican chorizo: Place a skillet over medium-high heat. Add the chorizo and cook, breaking it up with a spoon, until browned and crumbly, about 5-10 minutes.
You can cook the chorizo ahead of time since it'll warm through with the vegetables. You can also start this recipe by cooking the chorizo in the skillet, then add the vegetables (using the chorizo grease as the fat instead of vegetable oil), and proceed as directed.