Combine onion, bell pepper, and water in large nonstick skillet. Cook, covered, stirring occasionally until water is evaporated and vegetables are very tender, about 8 minutes. Transfer to large bowl; let cool 10 minutes.
Add chicken, Buffalo wing sauce, and salt to vegetables in bowl; mix well. With damp hands, shaped into 8 ( ½ -inch thick) patties. Cover with a piece of plastic wrap and chill until firm, at least 1 hour or up to overnight.
Coat skillet with oil and set over medium heat. Add patties and cook until instant-read thermometer inserted into side of burger registers 165 degrees F for well done, approximately 4 minutes per side.
Pull some of the bread from centers of buns. Place lettuce on bottoms of buns; top each with 1 burger, 1 tomato slice and scant 1 teaspoon blue cheese. Cover with tops of buns