Pat chicken dry and season with pepper.
Sprinkle chicken with corn starch and evenly coat.
Quarter lime.
Cut cucumber in half lengthwise and slice crosswise.
Thinly slice scallions, separating whites from greens.
Combine cucumber, scallion whites, rice vinegar, and 1 tbsp of sesame seeds, 1 tsp sugar, and a pinch of salt and pepper in a bowl and mix well.
Cook rice according to package instructions. Set aside.
Combine soy sauce, 4 tsp sesame oil, 8 tsp sugar, and 3 tsp sriracha in a bowl and mix well.
Heat oil in a large pan over medium heat. Add chicken and cook until browned and cooked through.
Once chicken is done, turn off heat and remove chicken from pan. Add the soy sauce to pan and let it bubble using the residual heat.
Return chicken to pan and mix to coat.
Fluff rice and stir in remaining sesame oil, a squeeze of lime juice, and half the scallion greens. Season with salt and pepper and mix.
Divide the rice, chicken, cucumber salad into bowls. Drizzle any remaining sauce, sprinkle with sesame seeds, and add sriracha to taste. Sprinkle with sesame seeds and remaining scallion greens. Serve with lime wedges.