Juice the limes and lemon and combine them in a cup.
To a blender or food processor add the garlic, cilantro, jalapeno, half the cucumber, half the citrus juice, and salt. Blend until smooth.
Add the shrimp to a bowl. Pour on the remaining citrus juice and aguachile from the blender, then add the onions and remaining cucumber and stir to combine.
Cover and chill in the refrigerator for 30 minutes.
Once the shrimp has "cooked", stir in the avocado. Sprinkle tajin over the top. Serve with tortilla chips and enjoy.