In a large mixing bowl, combine the yogurt, olive oil, lemon juice, salt, black pepper, thyme (or oregano), paprika, and chili flakes. Mix well to create a smooth marinade.
Pat the chicken thighs dry with a paper towel. Add the chicken thighs to the bowl with the marinade, ensuring each piece is well-coated.
Cover the bowl with plastic wrap and refrigerate for at least 2 hours, preferably overnight for maximum flavor.
Preheat your grill to medium-high heat (about 375-400°F or 190-200°C). Lightly grease the grill grates with oil to prevent sticking.
Remove the chicken thighs from the marinade, letting any excess drip off. Place the thighs skin-side down on the grill over direct heat.
Grill for 5-7 minutes per side, or until you have a nice char on the outside.
Move the chicken thighs to indirect heat and continue grilling for another 10-15 minutes, or until the internal temperature reaches 165°F (75°C).
Remove the chicken thighs from the grill and let them rest for 5 minutes before serving.