In a small iron skillet toast the coriander and cumin for a few seconds or until the spices emit a lovely aroma. Remove from heat and cool for a moment. In a small mixing bowl combine the toasted spices with the paprika, lime juice and sugar. Season with 1 teaspoon salt and crushed red pepper.
Prick the chicken pieces all over and rub the pieces with half of the lime/spice mixture. Combine remaining half of lime/spice mixture with garlic, vegetable oil and yogurt. Marinate the chicken in the yogurt mixture for 24 hours, turning the pieces on occasion.
Preheat the broiler (or heat an outdoor grill) and set the rack 4 inches away from heat source. Remove chicken from marinade and broil, skin side down for about 15 minutes a side or until cooked through and browned. Let rest at room temperature for up to an hour before serving. Or chill and bring back to room temperature before serving.