Wash and dry all produce. Halve zucchini lengthwise; slice crosswise into thin half-moons. Trim and thinly slice mushrooms. Trim and thinly slice scallions, separating whites from greens. Peel carrots; shave lengthwise into ribbons, rotating as you go, until you get to the core. Discard core. Peel and mince ginger. Mince garlic.

In a small pot, combine rice and 11/4 cups salted water (21/4 cups for 4 servings). Bring to a boil, then cover and reduce heat to low. Cook until rice is tender, 15-18 minutes. Turn off heat; keep covered until ready to serve.

Meanwhile, in a small bowl, combine scallion whites with vinegar and a pinch of salt. Set aside to quick-pickle. In a separate small bowl, combine sesame oil, half the soy sauce, 1 TBSP sugar (2 TBSP for 4 servings), and as much sriracha as you like.

Heat a drizzle of oil in a large, preferably nonstick, pan over mediumhigh heat. Add carrots and season with salt and pepper. Cook, stirring, until just tender, 3-4 minutes. Transfer to a medium bowl. Add zucchini and another drizzle of oil to pan. Cook, stirring, until tender, 4-5 minutes. Transfer to bowl with carrots. Add mushrooms and another drizzle of oil to pan. Cook, stirring, until tender, 3-5 minutes. Season with salt and pepper. Transfer to bowl with other veggies.

Heat another drizzle of oil in same pan over medium-high heat. Add garlic and ginger. Cook, stirring, until fragrant, for 30 seconds. Add beef and cook, breaking up meat into pieces, until lightly browned, 3-4 minutes. Drain any excess grease from pan. Increase heat to high and cook until browned, crisp, and cooked through, 2-3 minutes. Stir in remaining soy sauce and cook until mostly evaporated, 1-2 minutes. Season with salt and pepper.

Fluff rice with a fork; divide between bowls. Arrange beef, zucchini, carrots, and mushrooms on top. Top with pickled scallion whites (draining first). Drizzle with sauce and any remaining sriracha to taste. Sprinkle with scallion greens and serve.