Roast the chile poblano on an open gas flame, or under a broiler. Make sure that it is dark and well blistered all over, but not black and ashy. Roasting should take 3 to 5 minutes. Wrap the roasted chile in a clean dry kitchen towel, and place in a paper bag. Allow the chile to sweat in the towel and bag for about 15 to 20 minutes, until it is somewhat cooled.
Remove the chile from the towel, and then peel off the blackened skin. Rinse under running water, remove the top stem, slice open and remove the seeds. Slice into strips and set aside.
Heat the vegetable oil in a 12-inch skillet for about 60 seconds. Add the butterflied steaks, and cook for 3 to 4 minutes, then flip and cook for another 3 to 4 minutes. Season with salt and pepper. Remove the steak to a plate.
Add the chile strips and the sliced onions to the pan, and sauté for 2 to 3 minutes, until the onions are translucent. Salt and pepper to taste, and then place half of the onions and peppers on top of each steak. Serve immediately.