Peel and devein the shrimp, leaving the tails on for added crunch. Place them in a mixing bowl.
Squeeze fresh lime juice over the shrimp until they're fully submerged. Toss gently to coat all the pieces evenly.
Chop the red onion into thin slices and add to the bowl. Mix everything gently, then let it marinate in the fridge for 15-20 minutes until the shrimp turn opaque and firm.
While the shrimp is marinating, chop fresh cilantro just before adding. Dice tomatoes and finely chop the jalapeño, removing seeds for less heat. Set aside.
Once the shrimp has turned opaque and firm, remove the bowl from the fridge. Stir in the chopped cilantro, diced tomatoes, and jalapeño.
Season with salt and pepper to taste, adjusting the acidity and flavor as needed. Toss everything gently to combine.
Serve the ceviche chilled, with tortilla chips or spooned directly into bowls. Enjoy the bright, oceanic flavors with a satisfying crunch.