In a small bowl, whisk together the rice vinegar, fish sauce, agave nectar and chili garlic sauce.
Prepare a bowl of ice water.
Set a large saucepan of water over high heat, and bring the water to a boil. Add the shrimp and boil until the shrimp is just cooked through, 60 to 75 seconds. Drain and immediately plunge the shrimp into the ice water to stop them from cooking further. Drain
In a medium bowl, mix together the shrimp, cucumber, avocado and cilantro. Pour in the dressing and toss to combine. Serve.