In a medium size bowl, stir together garlic, salt, sugar, cilantro, jalapeno, celery seed, pepper, lime juice and zest as well as the rice wine vinegar.
Whisk in the olive oil to the mixture to create the marinate.
Place the shrimp and onions in the bowl and toss with the marinate. Cover the bowl with plastic wrap or lid and set in the refrigerator for 24 hours for the flavors to meld. Stir the ingredients a couple of time during the process.
Just prior to serving, peel the avocado and cut into half inch cubes. Season the avocado with a little salt and pepper.
Serve the shrimp chilled, alongside the diced avocado and tortilla chips.