Preheat the oven. Set it to 425°F (220°C). A hot oven helps finish the chicken quickly and keeps the skin crisp.
Dry the chicken well. Pat the thighs very dry with paper towels, especially the skin. Dry skin equals crisp skin.
Season generously. In a small bowl, mix Cajun seasoning, salt, pepper, garlic powder, smoked paprika, and brown sugar if using.
Rub 1 tablespoon of oil over the thighs, then coat all sides with the spice mix. Lift the skin slightly and season underneath for deeper flavor.
Heat the pan. Place your skillet over medium-high heat and add the remaining oil. When it shimmers, it’s ready.
Sear skin-side down. Lay thighs in the hot pan, skin-side down.
Don’t crowd; work in batches if needed. Sear 5–7 minutes without moving, until the skin is deeply golden and crisp.
Flip and finish in the oven. Turn the thighs skin-side up. Transfer the skillet to the oven and roast 12–18 minutes, depending on size, until an instant-read thermometer in the thickest part reads 165°F (74°C).
Rest and brighten. Let the chicken rest 5 minutes.
Squeeze a little lemon over the top and scatter chopped parsley or green onions if you like.
Serve. Pair with creamy mashed potatoes, Cajun rice, cornbread, or a cool slaw. A dollop of plain yogurt or ranch also plays nicely with the spice.