Place the chicken on a cutting board and cover with wax paper. Using a meat mallet or bottom of a skillet, give each breast about 10 whacks to help tenderize the meat, or until the breasts are a uniform 1/2 inch thickness.
Place the tenderized chicken breasts in a large bowl or ziplock bag with the remaining chicken ingredients (olive oil, coriander, paprika, cayenne, curry powder, cumin, coconut milk and lemon juice). Toss or shake until well combined and the chicken is well coated. Cover and refrigerate for at least 1 hour prior to grilling, or up to overnight.
In a small jar or bowl, combine all of the herb vinaigrette ingredients. Shake (or whisk) until well combined. Set aside until ready to serve.
Assemble the butter lettuce leaves across the bottom of a large platter or bowl. Top with onions, tomatoes, and cucumbers. Set aside.
After the chicken has marinated, heat a grill over medium-high heat. When hot, place chicken on the grill, cover and cook for 4 to 5 minutes, or until nice grill marks form. Flip, cover and continue cooking until the chicken is cooked through and a nice, golden brown grill marks have formed. Remove from heat and let rest for 5 minutes before serving.
Finish the salad by drizzling and gently tossing with desired amount of the herb vinaigrette. Top with the chicken breasts, and finish by garnishing with fresh cilantro. Serve and enjoy!