Cut the chicken breasts horizontally without cutting all the way across. You want to be able to fan the chicken open, keeping the tender underneath (the breast is more likely to split in two if you remove the tender).
Cut a small notch in the middle of the thick end–just enough to make the heart shape. You should not have to do much shaping. I remove just a little from the top of each side, right in the center.
If you are using a rub, sprinkle it over both sides of the breast. If you are using chicken that you have marinated, remove from the marinade.
Heat an oiled skillet over medium to medium-high heat. When hot, place the chicken breast, tender side up first and cook for about 3 minutes. Then, flip and cook for 3-5 minutes, depending on size of breast, until chicken is just cooked through the center. If you are using barbecue sauce, baste the cooked chicken with sauce on both sides and flip a couple of times in the hot skillet to caramelize the sauce a bit.
Place the spinach or mixed greens on a plate and top with avocado, tomato, red onion, and chicken (sliced or cut into bite-size pieces, if desired). Drizzle with dressing and enjoy!
