Preheat the oven to 425°F (218°C). Spray an 8×8-inch or 9×9-inch baking dish with cooking spray and set aside.
In a small bowl, combine 1/2 cup packed light brown sugar and 1 packet dry Italian dressing mix; stir until evenly blended.
Pat the chicken thighs dry with paper towels. Evenly sprinkle the brown sugar mixture over all sides of the chicken, pressing gently so it adheres. If any rub remains, sprinkle it over the top of the chicken.
Place the coated chicken pieces in the prepared baking dish in a single layer. If adding vegetables (optional), use a 9×9-inch dish and arrange them around the chicken.
Bake for about 25 minutes, or until the internal temperature of the chicken reaches 165°F (74°C) when measured with an instant-read thermometer.
Optional: For a slightly crisped top, broil 1–2 minutes, watching carefully to prevent burning because the sugar can char quickly.
Let the chicken rest briefly before serving. Optionally garnish with fresh herbs and season with salt, pepper, or red pepper flakes to taste.
