Saute chopped onion in a little butter or olive oil until translucent. Set aside.
Place peppers on pan and broil or grill on high heat for about 3-4 minutes, flipping once. Put blackened peppers in brown paper bag and close it, leaving to stand for about 15 minutes.
Brown chorizio sausage for about 10-15 minutes in a skillet until well done, breaking it up along the way. Set aside.
Take peppers out of paper bags, and peel off skin (it should be easy because of the steaming in the bag). Slice peppers in large wide strips.
Place pepper strips in bottom of small cast iron skillet or oven-proof dish. Cover with a layer of about 1/2 of the grated cheese. Cover the cheese with the sauteed onions. Cover with remaining cheese.
Sprinkle the chorizio on top.
Bake in oven at 400 degrees for about 15 minutes, until cheese is melted and beginning to turn golden.
Serve immediately with warm tortilla chips and salsa.
