In a large mixing bowl, combine turmeric, a pinch of saffron, fresh lemon juice, olive oil, minced garlic, chile flakes, salt, and pepper. Whisk until smooth.

Add chicken thighs and sliced onions into the marinade, ensuring even coating. Cover or transfer to a resealable bag and marinate for at least 30 minutes.

Preheat the grill to medium-high heat (400-450°F) for even cooking.

Carefully remove the chicken from the marinade and place skin-side down on the grill. Cook for 6-8 minutes until golden brown, then flip and grill the other side for another 6-8 minutes or until the internal temperature reaches 165°F.

For the onions, use a grill basket and cook alongside the chicken for 8-10 minutes until charred and tender.

Remove the chicken and onions from the grill, let the chicken rest for a few minutes before serving.