Whisk all the ingredients for the dressing/marinade in a medium bowl. Pour half the mixture onto the chicken breasts and coat chicken breasts with the marinade well. Cover and place in the fridge for 30-minutes or up to 24 hours or use immediately. Reserve the rest of the marinade for later to be used as a dressing.
Heat a large heavy-duty pan or skillet to medium-high heat for 2 minutes. Add a teaspoon of oil to the pan and then add in the chicken breasts. Cook 4-5 minutes per side or until cooked through. Remove from pan onto a cutting board and cool for 5 minutes then slice or chop into bite size pieces. Add the sliced bell peppers to the pan. cook on high for 1-2 minutes or until charred.
Divide romaine lettuce into two salad bowl. Top each salad with half the chicken, fajita veggies, and sliced avocado. Serve with reserved dressing and sour-cream if desired. Enjoy the salad warm!