Mix the five-spice powder, the 1 tablespoon sugar, the garlic powder, and the salt in a small bowl. In another bowl, mix the soy sauce, vinegar, sesame oil, red pepper flakes, and remaining 1 teaspoon sugar.

Put the chicken in a shallow pan, drizzle with the vegetable oil, and toss to coat evenly. Sprinkle the spice mixture over the chicken; toss and rub to coat thoroughly.

Prepare a hot charcoal fire or heat a gas grill with all burners on medium high for 10 minutes. Clean the hot grate with a wire brush and then lubricate it with an oil-soaked paper towel. Put the chicken on the grate and grill (covered on a gas grill or uncovered over a charcoal fire) until one side has dark grill marks, 5 to 6 minutes for large thighs or 4 to 5 minutes for medium and small thighs. Turn and continue to grill until well marked on the other sides and cooked through, 5 to 6 minutes longer for large thighs or 4 to 5 minutes for medium and small thighs.

Move the thighs to a serving dish. Drizzle with about half of the soy mixture, sprinkle with the cilantro, and toss to coat. Let rest 4 to 5 minutes, tossing once or twice. Serve hot, warm, or at room temperature, with the remaining soy mixture passed at the table.

To prepare as kebabs: Trim the thighs and then slice them lengthwise into 1-1/2- to 2-inch-wide strips. Toss with the flavorings; then thread the chicken onto six 8- or 12-inch skewers (soak wood skewers in water for at least 20 minutes first), folding each strip in half as you skewer it. If some strips are very thick, cut them in half crosswise rather than folding them so that all the pieces of chicken are roughly the same size. Grill the kebabs, turning them every 4 to 5 minutes as dark grill marks form, until cooked through, 12 to 15 minutes total