Combine the soy sauce, sugar, scallion whites, garlic and sesame oil in a large bowl; add the steak and let marinate 10 minutes. Preheat a large nonstick skillet over high heat. Add the steak and marinade and season lightly with salt and pepper. Cook, undisturbed, until the steak starts browning around the edges, about 3 minutes. Stir and continue cooking until the steak is just cooked through, about 2 more minutes. Remove to a bowl.
Heat 2 teaspoons vegetable oil in the skillet. Add the rice, season with 1/2 teaspoon salt and cook, stirring occasionally, until slightly crisp, about 3 minutes. Stir in the spinach until just wilted. Add the steak and any juices from the bowl; heat through. Remove from the heat and stir in the bean sprouts; season with salt and pepper. Divide among bowls.
Wipe out the skillet, return to high heat and add the remaining 2 teaspoons vegetable oil. Crack in the eggs, season with salt and cook until the whites are set but the yolks are still runny, about 3 minutes. Top each rice bowl with an egg and the scallion greens. Drizzle with Sriracha.