In a mixing bowl, combine 1/4 cup full-fat plain Greek yogurt, 2 tablespoons olive oil, 1½ teaspoons kosher salt, 1 teaspoon garam masala, 2 teaspoons ground paprika, 1/2 teaspoon ground turmeric, 1/2 teaspoon ground cumin, 1/2 teaspoon ground coriander, 1/2 teaspoon garlic powder, and 1/4–1/2 teaspoon chili flakes; stir until smooth and evenly blended.
Rub the yogurt-spice mixture all over 1½ pounds bone-in, skin-on chicken thighs, coating them thoroughly; place the thighs in a bowl or container, cover, and refrigerate for at least 2 hours or up to 24 hours.
When ready to cook, preheat the oven to 425°F (220°C). Line an 8×8-inch baking pan with parchment paper or foil and arrange the marinated thighs skin-side up in a single layer.
Bake for 30–35 minutes, until the juices run clear and the internal temperature reaches 165°F (74°C).
For crisper skin, switch the oven to broil and broil the thighs 1–2 minutes more, watching closely to avoid burning.
Remove the chicken and let rest 10 minutes before serving; sprinkle with chopped cilantro and serve with lime wedges if desired.