In a small bowl, whisk together the garlic, vinegar, soy sauce, sesame oil, and chili oil (if using). Taste and season with a pinch of salt if needed.
Prep the vegetables: Pit, peel, and slice the avocado; cut the cucumber; slice the red onion; and chop the cilantro.
Toss the cucumbers, avocado, red onion, and cilantro in a bowl with the dressing. Finish with toasted sesame seeds, if desired and enjoy!
