COMBINE mayonnaise, mustard, and vinegar to make dijonnaise. Mixed until homogeneous. Set aside.
BRING a medium-sized pot of salted water to a rolling boil. Add green beans and cook for 3-4 minutes to achieve the desired texture. Strain well and set aside.
REMOVE Whole30 Italian-Style Chicken breast from the fridge and slice into strips.
HEAT chicken in a skillet over low heat, just to heat through, or in the microwave for 60-90 seconds.
IN a large mixing bowl, toss green beans in the prepared dijonnaise until dressing is evenly distributed.
DIVIDE the green bean mixture onto three plates, top with the sliced chicken and enjoy!