Whisk together all the ingredients for marinade dressing. Marinate the chicken in half the dressing for 10 minutes, reserving the rest for the salad.
Heat a grill pan and place the chicken breasts on it. Cook on each side for 4-5 minutes. Let the chicken rest for 10 minutes and then slice.
In the same grill pan, add the red bell peppers and onions along with a tablespoon of the dressing and grill on high heat till lightly charred. Remove and set aside.
To assemble the salad, place roughly torn romaine lettuce at the bottom of the bowl. Place red bell peppers, onions, chicken and mango salsa (if using) on top. Drizzle with the remaining dressing. Toss and enjoy!