In a 9-inch cast-iron skillet, heat the olive oil over medium heat. Add the chorizo and cook, crumbling it as you go, until browned and cooked through.
Remove the chorizo from the skillet and drain it on paper towels (chorizo is very greasy!). Pour off any excess fat from the skillet.
Without cleaning the skillet, add the onion and bell peppers.
Cook the veggies over medium-high heat, stirring frequently, until they brown and soften, about 5 minutes. Turn off the heat and stir in the tequila, if using. Turn the heat back on to medium-high and cook until the vegetables are golden brown and the liquor has reduced, 2 to 3 minutes more. Remove the vegetables from the skillet and set them aside. Turn off the heat.
Mix the cheeses together, then cover the bottom of a medium ovenproof skillet with one-third of the cheese mixture . . .
Add one-third of the vegetables . . .
And one-third of the chorizo.
Continue with two more layers, ending with chorizo. Sprinkle the top with chili powder.
Bake until the cheese is totally melted, hot, and slightly bubbling around the edges, 4 to 5 minutes. Watch it constantly, as you don't want the cheese to get overly melted and hard. But you want it to be sizzling!
Top with the tomatoes, a sprinkle of kosher salt, and the cilantro.
Serve immediately with tortilla chips . . .
Or carrot sticks and cauliflower florets if you want to avoid chips!
Use any combination of melting cheeses you'd like.
Add chopped mushrooms to the onion-pepper mixture.
Use pork sausage instead of chorizo for a milder flavor.