Peel and devein the shrimp, then rinse them under cold water and pat dry. Place them in a large bowl.
Squeeze fresh lime juice over the shrimp until they are fully submerged. Toss gently to coat and set aside to marinate for 10-15 minutes until the shrimp turn opaque and firm.
While the shrimp marinate, thinly slice the red onion and dice the tomatoes. Prepare the jalapeño by mincing it finely, removing seeds if you prefer less heat.
Chop the cilantro coarsely and set it aside. Once the shrimp are opaque and firm, drain off excess lime juice if desired.
Gently fold the diced tomatoes, sliced onions, chopped cilantro, and minced jalapeño into the marinated shrimp in the bowl. Drizzle with olive oil if using, and toss to combine all ingredients evenly.
Taste the ceviche and adjust seasoning with more lime juice or salt if needed. Chill in the fridge for another 10 minutes to let flavors meld.
Serve the shrimp ceviche cold, garnished with additional cilantro or lime wedges if desired. Enjoy the bright, fresh flavors and crisp textures in every bite!