Preheat oven to 400ºF.
In a small bowl mix together the spice blend: garlic powder, paprika, salt, and pepper.
In a large bowl combine vegetables: cauliflower or broccoli, green beans, carrots, potatoes, red onion with oil and spice blend. Pour onto rimmed baking sheet and bake for 25 minutes.
Meanwhile place chicken breasts into the large bowl used for the vegetables and add sprinkle with salt and pepper.
In a small bowl, mix together the mustards, honey, and apple cider vinegar. Brush onto chicken and let marinade while your vegetables are cooking.
After 20 minutes take out the sheet pan and move vegetables to the sides to make space for the chicken. Place the chicken breasts in the middle of the pan and pour over any reserved marinade.
Continue to bake for 15 minutes, or until chicken is fully cooked through.
Remove from the oven and serve hot with pan juices! Sprinkle veggies with additional salt and pepper as desired, and any herbs!
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days or frozen for up to 3 months.