Combine warm water and kosher salt together in a glass dish. Stir until the salt dissolves. Add chicken and let sit at room temperature for 15-30 minutes while you prep the rest of your ingredients. Remove chicken from the brine, rinse in cold water and pat dry.
Meanwhile, whisk together honey mustard sauce ingredients in a small bowl. Remove 1/4 cup to coat chicken before it bakes - save the rest of the sauce for after the chicken bakes. Set aside.
Add potatoes to a microwave safe dish. Add enough water to fill 1/4” up the sides. Cover, and microwave for 6 minutes. Drain water and add potatoes to a lightly greased 9x13 baking dish. Add one tablespoon olive oil, 3/4 teaspoon salt and 1/4 teaspoon pepper. Toss to evenly coat then divide potatoes in half and push to the sides of the pan, making room for the green beans down the middle (see photos in post).
While the green beans are on the cutting board, toss with 1 tablespoon olive oil, 1/4 teaspoon salt and 1/8 teaspoon pepper. Line green beans down the center of the pan in between the potatoes (they will not be in a single layer but slightly overlapping).
Add 1 tablespoon olive oil and all “chicken seasonings” to a large bowl; stir together to make a wet rub. Add chicken and massage spices into the chicken with hands. Using the 1/4 cup reserved Honey Mustard Sauce, coat both sides of the chicken evenly in sauce. Transfer chicken to baking dish, and spoon over any remaining sauce/spices from the bowl.
Cover pan with foil and bake at 400 degrees for 25 minutes. Uncover and check for doneness with a meat thermometer. If needed, continue to bake, uncovered, an additional 10-20 minutes OR until chicken is cooked through (an instant read thermometer should register 165 degrees F, cooking time may be more or less depending on thickness of chicken). Let chicken rest 5-10 minutes before slicing chicken. Serve with remaining Honey Mustard Sauce.