In a small bowl, combine honey, whole grain mustard, Dijon mustard, 2 tablespoons of olive oil, and garlic. Whisk until fully blended. Transfer half of the dressing to a clean bowl, cover, and refrigerate until ready to serve.
Add the chicken to a large bowl. Pour the remaining dressing over the chicken and toss to coat. Cover and refrigerate for at least 1 hour, preferably overnight for maximum flavor.
When ready to cook, heat the remaining olive oil in a non-stick skillet over medium heat. Once hot, add the chicken. Cook on one side for 4-5 minutes, then flip the chicken and continue cooking for 4-5 minutes, or until the internal temperature reaches 165°F.
Transfer the chicken to a clean plate and loosely tent with foil to keep warm. After about 5-10 minutes, cube the chicken and set aside while you assemble the salad