Season the chicken breasts with salt and pepper. Then grill or cook in a skillet until brown on each side, about 5-8 minutes per side. I like to use thinner chicken breasts so they cook all the way through as they brown.
Once the chicken breast are browned on both sides and almost done cooking brush with teriyaki sauce on one side then flip and brush the remaining side with teriyaki sauce. Or if you are using teriyaki chicken packages from the freezer, just thaw the chicken and grill.
Be sure to keep the teriyaki sauce you are brushing the chicken with separate from the sauce to put on the finished sandwiches, just to be safe. Just spoon some of the sauce into a bowl and use that to baste the chicken while grilling and keep the rest separate for spooning on the cooked chicken.
If you have room in your skillet add the pineapple slices while the chicken is finishing up cooking. If you are grilling the chicken add the pineapple to the grill in the last 5 minutes of cooking to brown the pineapple on both sides.
Once the chicken is done cooking and the pineapple slices are browned remove from skillet or grill. Let the chicken rest a few minutes.
Assemble the sandwiches, I like to add mayo to the bun than a slice of lettuce, a slice of tomato, a slice of pineapple and the chicken breast. I also add a spoonful of the teriyaki sauce to the chicken too.