For zucchini sauce, heat butter in a saucepan over medium heat, add zucchini in batches and stir occasionally until zucchini is tender, but butter and zucchini are not coloured (5 minutes). Transfer to a bowl with a slotted spoon. Add garlic to pan, cook until translucent (3-4 minutes), return zucchini to pan and keep warm.
Meanwhile, cook pasta in batches in salted boiling water until just cooked (3-4 minutes). Drain, reserving 300ml pasta water, and return pasta to pan with zucchini mixture. Add 100ml reserved pasta water, stir over medium heat (1 minute), then continue adding reserved pasta water 100ml at a time and stir until zucchini is very tender and liquid forms a thick sauce (2-3 minutes; you may not need all the reserved pasta water). Stir in basil and lemon rind, season to taste and serve hot with grated parmesan.