Mix the ingredients for the peanut sauce together in a bowl first and allow to stand until the rest is ready. It will take about 1/4 cup of water or more to thin it down.
Heat the oil and red pepper flakes in a large skillet over medium high heat. Fry the tofu on all sides until golden brown. Remove to a paper towel lined plate to drain. Season with salt and lots of black pepper.
Pour off most of the oil and heat the onions and large stems from the bok choy until softened and beginning to change color.
Add the rest of the leaves and stir fry until tender and bright green.
Return the tofu to the pan and pour over about half of the peanut sauce. Mix to coat.
Serve with the remaining peanut sauce and chopped peanuts for garnish.