01 - Combine flank steak slices with 1 tablespoon soy sauce and cornstarch in a medium bowl. Toss to coat and let sit for 10 minutes.
02 - Whisk together 3 tablespoons soy sauce, sriracha, hoisin sauce, brown sugar, rice vinegar, minced garlic, grated ginger, and sesame oil in a small bowl until smooth.
03 - Heat a large skillet or wok over high heat with a splash of oil. Sear beef in batches until browned and just cooked through, about 2 to 3 minutes per batch. Remove and set aside.
04 - In the same skillet, add more oil if needed and stir-fry bell pepper, snap peas, and carrot for 2 to 3 minutes until tender-crisp.
05 - Return seared beef to the skillet, pour in the prepared spicy sauce, and toss over high heat for 1 to 2 minutes to blend flavors and heat thoroughly.
06 - Spoon the beef and vegetable mixture over steamed jasmine or basmati rice. Garnish with sliced spring onions, toasted sesame seeds, and fresh cilantro if desired.