Place chicken breasts into a plastic resealable bag with soy sauce, seal the bag and marinate in refrigerator for 30 minutes. While chicken is marinating, place the bacon in a large, deep frying pan and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon on a kitchen towel-lined plate and set aside. Spread cut sides of burger buns with butter.
Preheat an outdoor barbecue for medium heat and lightly oil the cooking grate.
Remove the chicken from the soy sauce and discard the excess soy sauce. Place the chicken breasts onto the preheated barbecue and barbecue until chicken shows good barbecue marks, is no longer pink inside and the juices run clear, 4 to 5 minutes per side. When chicken is almost done, brush each piece generously on both sides with teriyaki sauce to finish barbecuing. Place a slice of Gruyere cheese on each chicken breast and cover with a lid to help the cheese melt onto the chicken.
While chicken is barbecuing, spread the buns open on the barbecue and cook until toasted and showing barbecue lines, about 2 minutes. Set the buns aside.
To assemble, spread the grilled sides of each bun with mayonnaise and top each bottom bun with a cooked chicken breast, 1 1/2 rashers of bacon, a slice of pineapple, a leaf of lettuce, a slice of tomato and the top bun.