Prepare the Sauce
In a small bowl, whisk together BBQ sauce, maple syrup, and soy sauce. Set aside.
Sear the Beef
Heat 1 Tbsp of oil in a large wok or skillet over high heat.
Add sliced beef in a single layer and sear for 2-3 minutes undisturbed.
Stir, season with salt and pepper, and cook another 2 minutes until almost done.
Add minced garlic and grated ginger, sauté for 1 minute, then remove the beef from the pan.
Cook the Mushrooms
Heat another tablespoon of oil.
Add sliced mushrooms, season lightly, and cook for about 5 minutes until golden.
Remove from the pan and set aside with the beef.
Stir-Fry the Vegetables
Add 1 Tbsp of oil to the same pan.
Toss in zucchini and bell peppers, cooking for 6-8 minutes over high heat.
Add onions and cook until softened but still vibrant.
Combine and Finish
Return the beef and mushrooms to the pan.
Pour in the prepared sauce and stir-fry until everything is well-coated and heated through.
Garnish with sesame seeds and serve hot.