Rinse the rice under cold water until the water runs mostly clear.

In a small saucepan, combine the rice, water and salt. Bring to a boil over high heat, then reduce to low, cover and cook until the water is absorbed and the rice is tender, 15 to 18 minutes. Remove from heat and let steam, covered, for 10 minutes. Fluff with a fork.

In a medium bowl, toss the red onions with the sumac. Add the lemon juice, olive oil, salt and parsley, and toss well. Let stand for at least 30 minutes.

In a large bowl, combine the chicken, yellow onion, 1 tablespoon harissa, the date syrup, paprika, cumin, salt and pepper. Toss to coat.

Heat the olive oil in a large skillet over medium-high. Add the chicken mixture and cook, stirring occasionally, until browned and cooked through, 8 to 10 minutes.

Stir together the remaining tablespoon harissa and the water, then add to the skillet. Cook, tossing, until the sauce lightly thickens and coats the chicken, 2 to 3 minutes. Stir in the parsley.

Serve the chicken over white rice and top with the sumac onions.