Whisk the sauce: In a small bowl, whisk soy sauce, water, brown sugar, rice vinegar, mirin, cornstarch, black pepper, and red pepper flakes until smooth. Set aside.

Prep the shrimp and veggies: Pat the shrimp dry with paper towels and season with a pinch of salt and pepper. Have all vegetables sliced and ready. Stir fry moves fast, so prep first.

Heat the pan: Place a large skillet or wok over medium-high heat. Add 1 tablespoon neutral oil and swirl to coat.

Sear the shrimp: Add shrimp in a single layer. Cook 1–2 minutes per side until just pink and slightly curled. Transfer to a plate. Do not overcook; they’ll finish in the sauce.

Stir fry the vegetables: Add remaining 1 tablespoon oil. Toss in broccoli and carrots first. Stir fry 2–3 minutes. Add bell pepper, peas, and the white parts of the green onion. Cook another 2 minutes until crisp-tender.

Add aromatics: Push veggies to the sides. Add garlic and ginger to the center. Cook 30 seconds until fragrant, stirring so they don’t burn.

Sauce it up: Give the teriyaki mixture a quick stir (cornstarch settles). Pour it into the pan. Stir constantly for 1–2 minutes until it turns glossy and thick.

Return shrimp: Add shrimp back to the pan. Toss to coat in the sauce and warm through, about 1 minute. Turn off heat and drizzle with sesame oil.

Finish and serve: Sprinkle with sesame seeds and the green parts of the green onion. Serve immediately over hot rice or noodles.