Step 1Heat the olive oil and onion over low heat in a large saucepan or straight-sided saute pan. Cook until the onion becomes translucent, about 3 minutes. Add the garlic cloves and cook until they begin to soften, about 4 to 5 minutes.
Step 2Add the cauliflower, white wine, white wine vinegar, salt, bay leaf, thyme, whole peppercorns and red pepper flakes. Cook until the cauliflower is tender but crisp, about 5 minutes.
Step 3With a slotted spoon, remove the cauliflower to a bowl and set aside. Add the green olives and lemon zest to the pan, increase the heat to high and reduce the liquid to a thick syrup, about 5 to 8 minutes.
Step 4Remove the bay leaf and pour the syrup over the florets. Cover tightly and refrigerate at least a couple of hours before serving. The cauliflower will keep for several weeks if refrigerated.