Chop shrimp into little bite size pieces. Place in a bowl or a baking dish; squeeze juice lemon and limes and everything is evenly mixed and covered in the juice. Set in the fridge for 2-3 hours, until shrimp is white and opaque. Let sit over night to absorb more flavor.
When shrimp is done, drain and place in a bowl. Add chopped cilantro, tomato, cucumber, onion and serrano peppers. Squeeze juice from one lime and one lemon and stir. Serve on a tostada shell, or with chips and enjoy!