Slice the scallops in half, patting them dry with a towel. Place in a glass bowl. Add red onion, tomato, lemon juice, lime juice, olive oil, salt, pepper and chili pepper. Mix and refrigerate for 2 hours, occasionally stirring to ensure all ingredients marinate evenly. Just before serving mix in the cilantro.
Serve on a plate, or in a glass as an appetizer. It can also be accompanied with a slice of lemon butter-grilled bread. Serves 4 - 6