Preheat oven to 425 degrees F.
Toss squash, potatoes, red onions, garlic, 2 teaspoons of the salt, 1 teaspoon of the pepper, sage, rosemary, thyme, and 3 tablespoons of the olive oil together in a large bowl. Turn out onto a greased rimmed 1/2 sheet pan. Roast in oven for 30 minutes.
Meanwhile, add the green beans, reserved tablespoon of olive oil, reserved ½ teaspoon salt, reserved ¼ teaspoon pepper, lemon wedges, and cayenne or crushed red pepper to the bowl and toss well.
Remove sheet pan from oven, toss root vegetable mixture, and scatter the bean mixture evenly over the top of the root vegetables. Roast another 20-30 minutes or until vegetables are both all tender and crispy. Taste and re-season if necessary.
Serve hot, warm, or at room temperature.