Heat oven to 400°F. Spray 13×9-inch (3-quart) baking dish with cooking spray.
Meanwhile, in 10-inch nonstick skillet, melt 2 tablespoons of the butter over medium-high heat. In small bowl, stir together brown sugar, Italian seasoning and 1/2 teaspoon of the salt. Sprinkle over chicken thighs.
Cook chicken thighs in skillet 3 to 4 minutes on each side or until golden brown and crispy.
Arrange chicken thighs, potatoes, onions and lemon slices in baking dish. Sprinkle with remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Melt remaining 1 tablespoon butter, and drizzle over mixture.
Bake 30 to 40 minutes or until potatoes are tender and juice of chicken is clear when thickest part is cut (at least 165°F).