Preheat the oven to 475? F. In a large skillet, toss the panko with the oil. Toast over medium-high heat, stirring occasionally, until golden brown, about 8-10 minutes. Transfer the toasted crumbs to a shallow dish or pie plate.
In a second shallow dish, whisk together the flour, garlic powder, salt, and cayenne pepper. In a bowl, whisk together the egg whites, water, mustard and thyme.
Spray a wire rack lightly with cooking spray and place over a rimmed baking sheet. Working in batches, dredge a few pieces of the chicken in the flour, then the egg whites, and finally the breadcrumbs to coat, shaking off the excess between each step. Lay the coated pieces on the prepared wire rack and repeat with the remaining chicken.
Spray the tops of the chicken pieces lightly with the cooking spray. Bake until the chicken is cooked through, 10-12 minutes. Serve warm.