Start by chopping the shrimp into small, bite-sized pieces, then place them in a large bowl.
Squeeze fresh lime juice over the shrimp until they are fully submerged. Toss gently to coat evenly.
Cover the bowl and refrigerate for at least 30 minutes, allowing the citrus to firm up the shrimp and develop bright aromas.
While the shrimp marinate, thinly slice the red onion and soak it in cold water for a few minutes to mellow its sharpness.
Drain the onion slices and chop the fresh cilantro finely; set aside.
Dice the cherry tomatoes if using, and chop the chili peppers, removing seeds if you prefer less heat.
Remove the marinated shrimp from the fridge and gently fold in the sliced onions, cilantro, chopped peppers, and tomatoes, if using.
Season with salt and freshly ground pepper, tasting and adjusting until bright and balanced.
Serve the ceviche chilled, garnished with extra cilantro or lime wedges if desired.