In a medium bowl, toss together onions, 1 tablespoon oil, 1 teaspoon grapefruit juice, and ½ teaspoon each salt and pepper. Spread onions onto a large rimmed baking sheet. Bake for 10 minutes.
In same bowl, toss together carrots, parsnips, garlic, remaining 1 tablespoon oil, remaining 1 teaspoon grapefruit juice, and remaining ½ teaspoon each salt and pepper. Toss together with onions on pan, and bake for 10 minutes.
Add grapefruit slices to pan, and bake 15 minutes more.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/roasted-root-vegetables-and-grapefruit/