Position the brussels sprouts long ways and shave them into thin slices using a knife.
Mix them in a bowl with the olive oil, garlic powder, ground fennel, salt, and pepper.
Place them on a parchment paper-lined baking sheet and roast for 20-30 minutes, until they have a nice browned coloring and are crispy. (Halfway through cooking, toss them around the pan using a spatula to get an even roast.) Season salt and pepper if needed before serving.