If the spinach wasn't pre-washed, wash the leaves in several changes of cold water. Rinse well and drain in a colander. Spin dry.
Use a sharp, thin-bladed paring knife or a truffle slicer to cut the garlic lengthwise into uniformly sized paper-thin slices. Place the slices in a large skillet and add the olive oil. Set the skillet over low heat and cook, stirring constantly, until the slices start to turn golden brown, about 5 minutes. Remove the chips with a slotted spoon and drain on paper towels.
Pile the spinach into the skillet and increase the heat to medium-high. Season with salt and pepper, to taste. Cook, stirring constantly, until wilted but not soft, 2 to 3 minutes. Season again if desired. Serve hot with the garlic chips sprinkled on top.