Heat a large pan or wok on medium/high heat and start to brown ground beef. While the beef is browning, make the teriyaki sauce: In a medium saucepan, combine, brown sugar, soy sauce, garlic, hoisin sauce, vinegar, sesame seeds, red pepper flakes, sriracha. Bring to a gentle simmer over medium heat. Start rice if serving.
In a small bowl whisk the cornstarch and 1/4 cup of water together to make a slurry. Lower the heat to the teriyaki, add the starch/water slurry to the saucepan and stir occasionally until desired thickness of sauce comes about. Set aside.
Once the ground beef is browned, drain most of the oil and add the beef to a bowl, set aside. Add chopped veggies to the hot pan you used for the beef. Add oil if needed. Sauté onions, garlic, ginger, peppers, mushrooms, zucchini, carrots, broccoli for about 5-8 minutes or until the veggies are fragrant and softened.
Once the veggies are softened and fragrant, add the beef back into the pan/wok with the veggies and pour the teriyaki sauce over everything. Bring it to a simmer, mix well and serve over rice or lettuce cups.