Working with 1 orange at a time, use a sharp knife to slice off both ends of the orange to reveal the flesh. Stand the orange upright on a cutting board, slice off the peel and pith following the contour of the fruit, then cut the orange crosswise and dice. Repeat with the remaining oranges, discarding any seeds.
In a mixing bowl combine the diced oranges with the olives, harissa, salt, oil, and cilantro. Season to taste with more salt and harissa, if desired, and serve.