Preheat oven to 425°F.
Dice chicken thighs into 1-inch cubes and place in a large mixing bowl. Add yogurt, tomato paste, lemon zest + juice, garlic, oregano, paprika, cumin, cinnamon, salt, and black pepper. Mix well.
Cover and marinate for at least 20 minutes on the counter, or up to 12 hours in the fridge for more flavor.
Line a baking sheet with parchment paper. Spread chicken into an even layer. Top with sliced red onion and lightly spray with olive oil.
Bake for 35–40 minutes, then broil for 3–5 minutes until the chicken edges are slightly charred.
Serve over rice, in pita bread, or on top of a salad.
