Preheat the oven to 450°F. Line a baking sheet with foil.
Cut the poblano peppers in half and remove the seeds. Place them cut-side down on the prepared baking sheet. Drizzle with olive oil and season with salt, pepper and the garlic powder.
Roast for about 15 minutes, or until the skins are lightly blackened and blistered. Remove from the oven and let cool for 5 minutes. Peel off the skins, dice the peppers, and set aside.
Divide the ground beef into 6 equal portions, about ? pound each. Shape each portion into a patty approximately 4 inches wide and 1 inch thick. Cover and refrigerate while the grill preheats.
Preheat the grill to medium-high heat, approximately 450–500°F. Lightly oil the grill grates to prevent sticking.
Place the patties on the grill over direct heat. Season with the remaining salt and pepper.
Grill for about 4–8 minutes, flipping halfway through, until the burgers reach an internal temperature of 160°F.
Place one slice of American cheese on each patty during the final minute of cooking. Place the buns cut-side down on the grill and toast for about 1 minute, watching closely to prevent burning.
Place each burger on a toasted bun and top with the diced roasted poblano peppers.
Serve immediately.
Notes
For food safety, cook ground beef burgers to an internal temperature of 160°F. Use an instant-read meat thermometer inserted into the center of each patty to check for doneness.Store leftovers in an airtight container in the refrigerator for up to 5 days.