Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper or foil for easy cleanup.
Make the marinade: In a bowl, whisk together olive oil, tomato paste, garlic, balsamic vinegar, salt, black pepper, cinnamon, and crushed red pepper flakes until smooth.
Marinate the chicken: Pat the chicken thighs dry and coat them evenly with the marinade. Let them sit for at least 15 minutes (or up to overnight for deeper flavor).
Roast: Place the marinated chicken thighs skin-side up on the prepared baking sheet. Roast for 35 minutes, or until the internal temperature reaches 165°F (74°C) and the skin is golden brown.
Rest & Serve: Let the chicken rest for 5 minutes before serving. Enjoy with maroulosalata, Mediterranean rice pilaf, and tzatziki for a delicious meal!
