In a small bowl, combine the tomato, serrano pepper, oregano, salt and pepper. Set aside.

In a large bowl, toss together the cheese with the flour until well coated. Set aside.

Set a large cast iron skillet over medium-high heat. Cook the chorizo, breaking up with a wooden spoon, until browned, about 8 minutes. Add the onion and continue to cook until softened. Remove with a slotted spoon and transfer to a plate.

Pour the beer into the skillet and bring to a simmer. Stir in the cheese, a handful at a time, until melted through. Remove from heat, stir in the chorizo and top with the salsa. Serve with warmed tortillas or chips on the side.