Cut the tempeh into equal cubes. Rinse the half bunch of bok choy, remove the tough lower end and chop into coarse pieces. Keep the harder white stems and softer green leaves separate from each other. Peel the piece of ginger and mince as finely as possible.
Heat a wok or sturdy frying pan. Sear the tempeh cubes on all sides until golden brown and crispy. Add the minced ginger and the white parts of the bok choy to the pan. Stir-fry on high heat for a few minutes until the stems begin to soften slightly.
Add the remaining green leaves of the bok choy and pour in the tablespoon of tamari. Stir everything immediately and well. Heat for another one to two minutes, just long enough to wilt the green leaves and evenly distribute the tamari over the ingredients.
Remove the pan from the heat and spoon the warm dish directly onto a plate. Coarsely chop the cashews with a knife and sprinkle over the meal as a final touch.