Rinse oranges in hot water. With a heavy-duty vegetable peeler, remove skin from one orange. Cut skin into thin strips. Squeeze juice from orange. Cut the other orange in half. Squeeze juice from one half and cut the other half into slices.
Heat olive oil in a deep skillet. Add chicken breasts and cook over high heat, turning once, about 6 minutes. Remove and transfer to a plate. Season with salt and pepper and keep warm.
Tilt pan so that fat drains to one side. Deglaze with sherry, scraping up browned bits with a wooden spoon. Add orange zest, orange juice and chicken stock. Bring to a boil and cook over high heat until reduced by 1/3.
Rinse mint, shake dry and pluck leaves. Set aside about 10 leaves. Finely chop remaining leaves and stir into sauce. Season with salt and pepper. Return chicken breasts to the pan. Cover and cook until chicken is done, about 10 minutes.
Transfer chicken to a serving dish, drizzle with sauce and garnish with mint leaves and orange slices. Serve with saffron rice, if desired.