1 medium yellow onion, sliced into 1/4-inch slices
2 cloves garlic, minced
1 1/2 pounds ground chuck
8 ounces chorizo, crumbled and cooked (browned in a skillet)
1 to 2 canned chipotle chilies in adobo, finely minced (seeded if desired)
8 thick slices Monterey Jack cheese
4 hamburger buns, lightly toasted
One at a time, use tongs to hold the chilies over a gas burner, turning until well charred, about 5 minutes. You also can set the chilies under a broiler for about 10 minutes, turning regularly. Place the chilies in a bowl, cover with a kitchen towel and let cool. Rub off the blackened skin and pull out and discard the stems and seed pods. Cut the chilies into 1/4-inch strips.
In a medium skillet over medium, heat the oil. Add the onion and saute until it begins to brown, 7 to 8 minutes. Stir in the garlic and poblanos and cook for 2 minutes. Season with salt, usually about 1/2 teaspoon. Transfer the mixture to a bowl and cover to keep warm.
In a large bowl, combine the ground chuck, cooked chorizo, chipotles and 1 1/2 teaspoons of salt. Mix until well combined. Divide the mixture into 4 equal portions and form into patties.
Heat a gas grill to medium-high, or light a charcoal fire and let it burn until the charcoal is covered with white ash (about medium hot); bank the coals to one side.
Place the hamburger patties on the grill and cook for a total of 4 to 5 minutes for medium rare. Lay one piece of cheese on top of each burger, top with the warm onions and chilies, then another piece of cheese. Close the lid of the grill and continue cooking until the cheese has melted, about 1 minute. Remove from the grill and slide onto a toasted bun.