In a large bowl, put the onion and lime juice for about 5 min.
Add the tomato, corn, beans, cilantro, diced chile and salt. Mix, taste, and adjust if necessary.
Set it aside.
To make the avocado crema, put the avocado, garlic, lemon juice, and salt in a blender container. Add 2 or 3 tablespoons of water so that it blends smoothly. Blend for 3-5 minutes until creamy.
If making romaine lettuce tacos. Simply put a tablespoon of pico de gallo on each lettuce leaf, a teaspoon of avocado cream, and a slice of chili serrano if you want an extra layer of spice.
If serving with chips, just put everything in serving bowls and dip the corn chips.
Notes
You can add the serrano pepper along with the other ingredients or put it on the side if not everybody likes the spice.You can also make avocado cream in a bowl by hand and without needing an electrical device. Crush the avocado with the back of a fork until it is entirely mushed and creamy. Add the minced garlic, lime juice, and salt.