Whisk soy sauce, rice vinegar, sugar, sesame oil, and black pepper in a small bowl; set aside.
Prep all veggies and pat them dry so they sear instead of steam.
Heat a large skillet or griddle over high heat until very hot.
Add the neutral oil. Sear broccoli and carrots, tossing, for 2 to 3 minutes.
Stir in onion and bell pepper. Cook until edges char slightly, about 2 minutes.
Add zucchini and mushrooms. Sear, stirring occasionally, 2 to 3 minutes until crisp-tender.
Push veggies to the sides. Melt butter in the center; sizzle garlic and ginger for 20 seconds.
Pour in the sauce and toss to coat. Cook 1 minute until glossy and reduced slightly.
Taste and season with salt if needed. Finish with sesame seeds and green onions.