Wash and dry all produce. Bring 21/2 cups water and a pinch of salt to a boil in a medium pot. Trim scallions, then thinly slice, keeping greens and whites separate. Trim any stems from green beans, then cut into 1-inch pieces. Core, seed, and remove ribs from bell peppers, then thinly slice. Mince garlic

Once water in pot is boiling, add rice, cover, and reduce to a simmer. Cook until tender, 15-20 minutes. Remove from heat and keep covered. Meanwhile, trim bottom inch and papery shoots from lemongrass. Peel off outer layers until you get to tender core. Finely mince core.

Cut steak against grain into thin strips. Toss in a medium bowl with cornstarch and a large pinch of salt and pepper until coated. Heat a drizzle of oil in a large pan over high heat. Add steak and sear until browned but not entirely cooked through, about 1 minute per side. Remove from pan and set aside

Heat another drizzle of oil in same pan over medium heat. Add garlic, lemongrass, and scallion whites. Cook, tossing, until softened, about 2 minutes. Add green beans and bell peppers and cook, tossing, until those are softened too, 5-7 minutes. Season with salt and pepper.

Add steak, soy sauce, vinegar, 3 TBSP water, and 1 TBSP sugar to pan. Cook, stirring frequently, until liquids have thickened and formed a smooth sauce, 1-2 minutes. Season with salt and pepper.

Fluff rice with a fork, then divide between plates. Top with stir-fry, then garnish with scallion greens and serve.