Season the chicken legs with salt, pepper, and paprika. Dip each leg in egg yolk, then coat thoroughly with sesame seeds. Fry in oil over medium heat for 15-20 minutes, turning occasionally, until golden brown and the internal temperature reaches 74°C (165°F).
For the sauce: squeeze the oranges into a bowl. In a saucepan over medium-high heat, caramelize sugar in oil for 2-3 minutes, then pour in the orange juice. Add stock and season to taste. Reduce over low heat for 5-10 minutes until slightly thickened.
For the couscous: bring stock to a boil, add 1 cup couscous and simmer covered for 5 minutes until tender. Chop the garlic and tomatoes finely, stir into the couscous, then mix in olive oil. Cool to room temperature.
For the onion salad: slice the onions into thin rings. In a bowl, whisk together vinegar, oil, salt, pepper, and sumac. Pour the vinaigrette over the onions. Cover and refrigerate overnight.