Heat up skillet over medium low heat (3 out of 10) to about 88ºC (190ºF), keep stirring constantly with flat wooden spoon. Once you hit the set temperature maintain the process for 15 minutes or until everything becomes a dry powder. Take off heat and transfer the mix to a medium size mixing bowl, set aside.
Note:
Temperature can go even higher up to 120ºC (248ºF) or even slightly higher and that is ok. Just lift the skillet of the heat for a few seconds and keep stirring. The idea is to completely dry out the arugula where it will become a light and crumbly powder, without burning it and while maintaining the cooking temperature as close to 88ºC as possible.