INGREDIENTS
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2 pounds small shell-on shrimp
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Kosher salt
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2 fennel bulbs, sliced crosswise  1/4-inch thick, fronds reserved
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1 English hothouse cucumber, sliced  1/4-inch thick
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1 small red onion, very thinly sliced into rings
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1 tablespoon finely grated lemon zest
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 1/4 cup (or more) fresh lemon juice
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Coarsely ground black pepper
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cup olive oil
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 1/2 cup small dill sprigs