Ingredients

• 1 pound shell-on medium shrimp
• Kosher salt
• 1/2 medium fennel bulb, thinly sliced
• 1/2 medium onion, thinly sliced
• 2 garlic cloves, thinly sliced
• 1/2 Fresno chile or red jalapeño, thinly sliced, seeded
• 1/2 cup fresh lemon juice
• 1/4 cup apple cider vinegar
• 1/4 cup extra-virgin olive oil
• 2 tablespoons fennel fronds
• Freshly ground black pepper
• 1/2 loaf ciabatta or country-style bread, sliced 1/2" thick, toasted
• Mayonnaise (for serving; optional)

Instructions

1. Cook shrimp in a large pot of boiling salted water until just opaque in the center, about 2 minutes. Drain; rinse under cold running water to cool. Peel and devein, leaving tails intact, if desired.
2. Combine shrimp, fennel bulb, onion, garlic, chile, lemon juice, vinegar, oil, and fennel fronds in a medium bowl. Season with salt and pepper and toss to combine. Let sit, tossing occasionally, at least 20 minutes.
3. Serve shrimp with toast and mayonnaise, if using.
4. DO AHEAD: Pickled shrimp can be made 2 days ahead. Cover and chill.