Heat a large cast iron skillet or wok over high heat. Add enough oil to coat the pan, waiting until it shimmers.
Add half the veggies to the pan and saute, undisturbed, for 1-2 minutes or until browned on the bottom. Sprinkle with salt and pepper. Toss, and cook another minute or so, until the edges have browned.. Remove to a plate, then repeat with the remaining veggies.
Add all the veggies back to the pan, and add the garlic and butter, allowing it to cook until fragrant, about 1 minute.
Add the sauce and cook, stirring frequently, until the vegetables have soaked up the sauce and are crisp tender, another 2-4 minutes. Remove from heat and sprinkle with sesame seeds if desired.