Combine chicken, green onions, bell pepper, cilantro, garlic, salt, red pepper flakes and juice of half a lime in a large bowl. Mix until thoroughly combined, then form into 4 patties and spray each side generously with non-stick spray.
Heat a large grill pan or skillet over medium-high heat. Grill burgers for 3-4 minutes a side, or until cooked all the way through. Place a slice of cheese on top of each burger, then cover with a large pot lid, and allow to melt for about a minute. Remove burgers to a plate, tent with foil, and allow to rest for 5 minutes. Place each burger on a toasted thin bun, then top with guacamole.
For the guacamole: Mash all ingredients together with a potato masher or fork.
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