Mix the sliced chicken with half of the peanut satay sauce and grated garlic. Let it rest for at least 30 minutes so the flavors absorb properly. If you have extra time, marinating longer makes it even better.
Combine cucumber, red onion, avocado oil, vinegar, salt, and sugar in a bowl. Toss gently until everything is evenly coated. Let it sit while you cook the chicken so the flavors develop.
Heat oil in a skillet over medium heat. Add the marinated chicken and let it cook undisturbed for a few minutes so it caramelizes nicely. Flip and cook until golden brown and fully cooked through.
Boil vermicelli noodles according to package instructions. Drain and rinse briefly under cool water to prevent sticking. Set aside until ready to assemble.
Divide noodles between serving bowls. Top with warm chicken and spoon the cucumber salad on the side. Drizzle with remaining peanut sauce thinned with a little water or soy sauce, then finish with herbs and crushed peanuts.