Heat the oil in a medium skillet over medium-high heat. Once hot, add the chorizo, cook for 4 to 5 minutes, breaking it into smaller pieces with a couple of spatulas or wooden spoons until crisp and brown. Remove from the heat and scrape into a bowl.
Set a rack on upper third tier of the oven and preheat to 450 degrees Fahrenheit.
Return the skillet to medium heat, add the butter and once it melts, add the onions. Cook, stirring occasionally and scraping the bottom of the pan, for 6 to 7 minutes, until they have wilted and begun to brown around the edges. Add the poblano pepper strips, tomato, and salt, and cook for another 3 to 4 minutes. Remove from the heat and transfer to a bowl.
Place shredded cheese in a gently oiled shallow baking dish that can comfortably hold it. Bake for 12 to 15 minutes, or until completely melted. Remove from the oven. Top with the crispy chorizo and poblano rajas mixture. Place back in the oven and bake for another 7 to 8 minutes, until cheese is oozing and browned along the edges and part of the top.
Meanwhile, preheat a comal or large skillet over medium-low heat. Heat the tortillas, making sure they are not on top of each other, until completely warmed, puffed and slightly browned. Place in a tortilla warmer or wrap in a clean cloth or kitchen towel.
Remove the queso from the oven and place on the table along with the warm tortillas, ripe avocado slices, and salsa of choice, if desired. Let everyone assemble their tacos!