Start by slicing the sirloin steak into thin strips against the grain.
In a bowl, combine the sliced beef with 1 tablespoon of sesame oil, kosher salt, and ground black pepper. Let it marinate for about 10-15 minutes.
Heat the remaining tablespoon of sesame oil in a wok or large skillet over medium-high heat. Add the sliced onion and cook for 2-3 minutes until translucent. Then, add the yellow squash, red bell pepper, and shiitake mushrooms. Stir-fry for another 3-4 minutes.
Add the minced ginger and garlic to the skillet. Stir continuously for about 1 minute until fragrant.
Add the marinated beef to the skillet. Stir-fry for 3-5 minutes, or until browned and cooked through.
Pour in the BBQ sauce, honey, and low-sodium soy sauce. Stir well to combine and let it cook for another minute or two until heated through.
Remove from heat and serve immediately over steamed rice, noodles, or on its own.