Using a mandoline or sharp thin-bladed knife, cut zucchini into very thin slices lengthwise; put in a large, shallow bowl.
With a vegetable peeler, shave ricotta salata cheese into narrow, thin slices. Tear squash blossoms into strips.
Season zucchini lightly with salt and pepper; toss gently. Drizzle with olive oil, then add juice from lemon. Taste and adjust the seasoning. On top, scatter cheese, then blossoms. Serve immediately.