In a large bowl, add yogurt, lemon juice, lemon zest, olive oil, garlic, tomato paste, dried oregano, 7-spice, turmeric, salt, black pepper, and optional chili flakes.
Whisk until the marinade is smooth and well combined.
Add the chicken cubes to the marinade and toss until evenly coated.
Cover and refrigerate for at least 1 hour, or up to overnight for best flavor.
Thread the marinated chicken onto metal or soaked bamboo skewers. Discard excess marinade.
Preheat and oil a grill. Grill the skewers, turning every few minutes, until fully cooked and lightly charred.
Chicken is ready when the internal temperature reaches 170°F (77°C).
Serve hot with your favorite sides.