On a baking sheet, toss together the chicken, olive oil, onion, garlic, parsley, chili powder, and a pinch each of salt and pepper. Add the lemon wedges.
Bake 15 minutes, toss and bake another 5-10 minutes, or until cooked through.
Meanwhile, make the feta sauce. Combine all ingredients in a food processor and blend until smooth. Season to taste with chili flakes, then top with mixed herbs and a drizzle of oil.
Switch the oven to broil. Broil 1-2 minutes, until the chicken chars on the edge.