Yes powder coating is usually a one coat process apart from when clear powder is used. The clear coat isnt any harder but 2 coats are better than one.
You could ask the powder coater to double coat ,the second coat is applied when the part has just left the oven and is still very hot the part is then restoved Doing it this way avoids paint defects such as static marks.
PS I worked for many years as a powder coater .