Set up your smoker and preheat it to 225°. I highly recommend including a water pan or water/drip pan to the lower rack of the smoker, under the meat. Use a digital oven thermometer to track the temperature on the grill grate.
Combine the seasoning in a bowl and whisk until evenly mixed.
While the smoker is preheating, rub each chicken breast with Dijon mustard and season them generously on both sides.
Insert an instant digital read thermometer probe into the center of the thickest chicken breast, through the side, to track internal temperature.
Place chicken breasts on the smoker when it’s ready and close the lid immediately. Smoke chicken until it reaches 160° and take it off the grill.
Tent the chicken with a sheet of aluminum foil loosely and let it rest for 5-10 minutes.