Bring 2 quarts water, kosher salt, lime wedges (squeeze juice out into pot as well as adding wedges), peppercorns and reserved cilantro stems to boil in a medium pot over medium-high heat. Add shrimp and cover; remove from heat and let stand 3 minutes, until just cooked through. Transfer with slotted spoon to ice bath.
When shrimp are cool, lift out of ice bath with slotted spoon. Pat dry and chop into 1/2-inch pieces; transfer to a large bowl.
To shrimp add tomatoes, cucumber, radishes, red onion, jalapeño, cilantro and lime juice; gently stir to combine. Season to taste with kosher salt and gently stir again. Cover and refrigerate 30 minutes.
When ready to serve, peel, seed and dice avocado. Add to ceviche and gently stir in to combine. Transfer to serving bowl and garnish with microgreens if desired. Serve with tortilla chips and lime wedges (optional).
Video
Notes
For a spicier version, leave seeds and membrane or use serrano chiles which tend to be spicier. Wear gloves when preparing raw chiles as their liquid can severely irritate your skin.
If you prefer a shrimp heavy ceviche: use 1/2 cucumber instead of a whole, 2 tomatoes instead of 4, and, optionally, reduce red onion to 1/4 cup.