Finely chop the garlic with the oregano leaves. Toss with the chicken and 1 tablespoon of the olive oil. For optimal flavor, marinate for at least 1 hour, but not absolutely necessary.
In a large pot, heat remaining oil. Add chicken and onion. Cook on high heat for 5 minutes stirring occasionally, until the onions turn translucent.
Add tomatoes, paprika, cinnamon, aleppo pepper, sugar and 5 cups water. Stir to combine. Bring to a boil.
Add orzo and cook for 10 minutes, stirring frequently with a metal spoon as the orzo has a tendency to stick to the bottom of the pot.
Add salt and pepper, to taste. Stir to combine.
To serve, garnish with sumac or a quick squeeze of lemon juice.
Notes
it's also often garnished with cheese, which gives it a nice creamy texture. Feta, Kasseri or even Parmesan can be used.