Cut chicken into 1 1/2 - 2" cubes. Heat oven to 350. Spray a 9x13" pan with non stick cooking spray.

In a shallow bowl combine the flour, garlic powder,  pepper, and salt. Dip each piece of chicken in flour mixture and coat evenly.

Pour melted butter in the 9x13" baking dish. Arrange chicken in a single layer in the butter, then flip to coat both sides.

Bake uncovered for 30 minutes.

Meanwhile, in a medium saucepan slowly whisk water into the cornstarch till dissolved. Add orange juice, vinegar, soy sauce, zest, brown sugar, ginger, and garlic. Cook and stir over medium high heat till mixture boils and thickens.

Remove chicken from the oven, turn each piece over, and pour sauce mixture evenly over chicken. Bake another 20-30 minutes, basting often.

Serve chicken and orange sauce over rice. Garnish with green onions and sesame seeds if desired.