Place the diced zucchini in a medium-size saucepan with the water; season lightly with salt and pepper. Bring to a boil and simmer, covered, over medium heat until slightly tender but still crunchy, about 2 minutes. Set aside without draining.
Heat the oil in a large skillet over high heat until hot but not quite smoking. Reduce the heat slightly; add the garlic and onion and cook, stir