Cook the Chorizo:

Preheat your oven to 375°F (190°C). Heat a cast-iron skillet over medium heat. Add the chorizo and cook, breaking it into small pieces with a spatula, until browned and fully cooked, about 5–7 minutes. Remove the chorizo from the skillet and set aside, leaving a bit of the rendered fat in the pan.

Sauté the Aromatics:

In the same skillet, add the diced onion and jalapeño (if using). Sauté for 2–3 minutes until softened and fragrant. Stir in the smoked paprika and cumin, cooking for another 30 seconds.

Layer the Cheese and Chorizo:

Reduce the heat to low. In a mixing bowl, combine the mozzarella, Monterey Jack, and cheddar cheeses. Spread half of the cheese mixture in the skillet, then layer with the cooked chorizo. Top with the remaining cheese.

Bake to Perfection:

Transfer the skillet to the preheated oven. Bake for 10–12 minutes, or until the cheese is fully melted and bubbling. For a golden top, switch to the broiler for the last 2–3 minutes, keeping a close eye to prevent burning.

Garnish and Serve:

Remove the skillet from the oven and let it cool slightly. Garnish with freshly chopped cilantro. Serve immediately with tortilla chips or warm tortillas.