In a large bowl, combine orange juice, lemon juice, garlic, olive oil, sugar, pepper, salt, oregano, and hot pepper flakes.
Divide the marinade in half and set aside half for the sauce.
Add the chicken cubes to the other half of the marinade and mix well.
Cover and refrigerate for 2 hours (or overnight), stirring occasionally.

Meanwhile, soak 25 wooden skewers (12-20 cm or 5-8 inches long) in water for at least 30 minutes (this will prevent them from burning).

Preheat the oven to 450 F (230 C).
Drain the chicken well. Thread one or two chicken cubes onto the end of each skewer.
Place the skewers on a baking sheet and cook in the oven for 5-10 minutes, or until the chicken is lightly browned.

In a small saucepan, combine the marinade that was set aside.
Cook over medium heat for about 10 minutes, or until it has reduced by half and there is only 1/2 cup (125 ml) left.
Strain the sauce and let it cool before stirring in the yogurt.
Divide the sauce among several small bowls and serve as a dip. Garnish with parsley.