Prepare the chicken. Remove any excess fat from the breasts and cut each breast into 2 pieces. Flatten each piece with a meat mallet or any heavy kitchen tool until the chicken has an even thickness. Season the chicken with the oil and all the seasonings.
Use a large pan over medium-high heat and wait for the pan to get hot. Once hot, add the chicken and cook for 10 minutes. Flip after 5 minutes.
Prepare the vegetables. Wash and dry the vegetables. Cut the romaine lettuce into 2 pieces per leaf. Cut the onion and tomatoes into about ¼ inch thick slices.
Assemble the sandwich. Toast the burger buns.Take each burger bun and add a tablespoon of mayonnaise. Place the chicken in the bun, the lettuce, tomato, and onion. Enjoy!
Notes
I used a potato bun, but you can use your preferred bread.
You can use whatever toppings and condiments you like.