In a bowl, combine soy sauce, honey, minced garlic, and a pinch of black pepper to create the marinade.
Place the lean beef sirloin in the marinade and let it rest for at least 20 minutes, allowing the flavors to infuse.
While the beef marinates, slice the red bell pepper, zucchini, and yellow onion.
Heat olive oil in a large skillet over medium heat.
Sauté the sliced onions until they soften, then add the red bell pepper and zucchini.
Cook the vegetables for about 5-7 minutes, stirring occasionally until they are tender but still crisp.
Remove the beef from the marinade and sear it in a separate hot pan over medium-high heat for about 3-4 minutes per side, or until it reaches your desired level of doneness.
Slice the beef into strips and serve over the sautéed vegetables, drizzling any remaining marinade on top if desired.