Heat oven to 400°F. Cut 18x12-inch sheet of heavy-duty foil; spray foil with cooking spray. In large bowl, toss beets, orange slices, oil, salt and pepper. Spoon mixture in center of foil. Bring up 2 sides of foil over mixture so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Place packet on cookie sheet.