Fill a large pot of water to a boil over high heat. Fill a medium bowl with ice water, set aside. Place the shrimp into the boiling water and cook just until opaque and pink all the way through, about 2-3 minutes. Drain and place the shrimp into the ice water to stop the cooking.
Once cooled, remove the shrimp from the water, dry with paper towels and cut into bite-sized pieces. Place them in a large bowl.
Add to the bowl with the shrimp the lime zest, juice, tomatoes, cucumbers, red onions, cilantro, salt, sugar, pepper, garlic powder, and cumin. Toss to combine and refrigerate until ready to use from 1-3 hours
Just before serving, mix in the avocado. Season to taste with salt.