PREHEAT the oven to 400°F. Line a large rimmed baking sheet with parchment paper.
COMBINE the onion powder, smoked paprika, garlic powder, 1/2 teaspoon salt, and 1/4 teaspoon black pepper in a small bowl
ADD the chicken to one side of the lined baking sheet, drizzle with 1 tablespoon of the olive oil, and toss to coat.
SPRINKLE the chicken with the seasoning and toss again.
PLACE the broccoli and potatoes, cut sides down, on the other half of the baking sheet. Drizzle with the remaining 1 tablespoon olive oil and sprinkle with the remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper. Toss to combine.
BAKE for 15 minutes, or until the chicken is cooked through (165°F), the broccoli is crisp-tender and lightly browned, and the potatoes are browned and tender.
STIR together the Buffalo sauce and clarified butter in a small bowl. Pour over the chicken and toss to coat. (Leave the vegetables on the baking sheet.)
RETURN to the oven for 5 minutes, until the sauce thickens slightly and the chicken looks glazed.
SPRINKLE the green onions over the chicken, broccoli, and potatoes and serve with ranch dressing.