Heat vegetable oil in a large cast iron or stainless steel skillet over medium-high heat until shimmering. Add half of onions and all of poblano and cook, stirring, until softened and starting to color, about 6 minutes. Add chorizo and cook, stirring and breaking up meat with a spoon, until completely cooked through and starting to crisp and char in bits, about 15 minutes total. Stir in chipotle chilies and remove from heat.
