1. Melt 1 TBSP butter in pot. Add half the sesame seeds and toast, stirring constantly, until fragrant and lightly golden, 30 seconds to 1 minute. Stir in rice, 2.25 cups water and pinch of salt. Bring to a boil, then cover and reduce to gentle simmer. Cook until water has absorbed and rice is tender, about 15 minutes. Turn off heat, keep covered until ready to serve.
2. Pat shrimp dry with paper towels. Season with salt and pepper. In bowl, whisk together soy sauce, cornstarch, 4 TSP sugar, half the sesame oil, 4 TSP water and half the Sriracha. Add shrimp and toss to thoroughly coat.
3. Wash and dry all produce. Trim, peel and halve cucumber lengthwise. Scoop out and discard seeds with a spoon. Slice cucumber crosswise into thin half moons. Trim and thinly slice scallions, separating whites from greens.
4. In a bowl, combine cucumber, scallion whites, vinegar, remaining sesame oil, 2 TSP sugar and a big pinch of salt and pepper.
5. Heat a large pan and add shrimp and 2 TBSP dressing from bowl with cucumber salad. Cook, stirring until mixture begins to thicken and shrimp is firm and cooked through, 3-4 minutes. Season with salt and pepper. Turn off heat.
6. Fluff rice with a fork and season with salt and pepper. Divide between plates. Serve with shrimp (and any remaining sauce from pan) and salad alongside. Sprinkle scallion greens and remaining sesame seeds. Drizzle with remaining Sriracha, if desired.