Preheat the oven to 400°F / 205°C. Mix 2 cups of shredded Oaxaca cheese and 2 cups of shredded Monterey Jack.
Cook 225g of raw Mexican pork chorizo, casing removed, in an ovenproof skillet for 5-7 minutes, breaking it up, until browned and cooked through to 160°F / 71°C. Transfer to paper towels and pour off excess fat.
Add 1 teaspoon of olive oil, ½ small white onion, minced, and 1 jalapeño, deseeded and diced. Cook for 6-8 minutes, until soft; remove from the skillet.
Layer half the cheese in the skillet, then all the chorizo, onion and jalapeño. Cover with the remaining cheese.
Bake for 8-10 minutes, until completely melted. Top with 1 Roma tomato, diced, and 2 tablespoons of chopped cilantro. Serve immediately with warm tortillas or tortilla chips.
