Dice the fresh fish into small, uniform pieces.
Place the fish in a bowl and cover it with fresh lime juice.
Let the fish marinate for about 15-20 minutes until it becomes opaque.
Finely chop the red onion, tomatoes, cucumber, and jalapeño.
Drain excess lime juice from the fish but leave a little for flavor.
Add the chopped vegetables and cilantro to the fish.
Season with salt to taste and mix gently.
Let the ceviche sit for an additional 5 minutes to meld flavors.
Serve chilled, garnished with avocado slices.
Enjoy your ceviche with chips or tostadas!