Preheat your oven to 400 degrees F. Coat a baking sheet with non-stick cooking spray or line with a silicone mat.
Cut the potatoes into 1-inch pieces and place in a mixing bowl. Toss in 1 1/2 tablespoons oil and seasoned salt until evenly coated. Place the potatoes on the baking sheet in an even layer.
Bake for 15 minutes while you prepare the rest of the recipe.
Cut each chicken breast in half horizontally (butterfly the thicker end of the chicken if desired). Coat one side of the chicken with half the ranch seasoning packet. Flip the chicken over and coat the other side with the remaining seasoning. Set aside
To the same bowl you seasoned the potatoes in, add the green beans, remaining oil, garlic, salt, and pepper. Toss until evenly combined.
Remove the baking sheet from the oven and carefully push the potatoes to one side of the pan so about 2/3 of the pan is free.
Place the chicken on 1/3 of the pan in a single layer, and the green beans on the other 1/3 of the pan in a single layer.
Bake for another 20 to 25 minutes, or until the chicken is cooked through and the potatoes are fork tender.
Carefully remove from the oven. Serve each person 2 chicken pieces, 1/4 of the potatoes and green beans. Serve immediately.
If you're not using the same bowl you mixed the potatoes in to mix the green beans, be sure to increase the salt to 1/2 teaspoon.