First make the dill Greek yogurt sauce. Combine the minced garlic, fresh dill, yogurt, olive oil, lemon juice and cayenne pepper in a food processor. Run the food processor until all the ingredients are well blended and a smooth thick sauce or dip develops. Test and add salt if needed. Transfer to a small bowl or container, cover and refrigerate.
In a small bowl, mix together the minced garlic, spices and 3 tbsp olive oil. Pat the chicken thighs dry and rub each with the garlic-spice mixture.
Place the spiced chicken thighs in a large dish on a bed of sliced red onions with lemon juice and the remaining 2 tbsp olive oil. Cover and refrigerate for 2-4 hours or overnight.
When ready, heat a gas grill to medium-high. Place the chicken thighs on the grill. Cover for 5-6 minutes, then turn the chicken over and grill for another 5-6 minutes covered.
Serve with a side of the dill Greek yogurt dip you prepared earlier!
To complete this light meal, add Greek potatoes or pita bread and a salad like Fattoush Salad.