In a medium bowl, combine the thinly sliced beef with soy sauce, sesame oil, minced garlic, and grated ginger. Allow it to marinate for about 10 minutes.
Meanwhile, prepare your vegetables by slicing the bell peppers, cutting broccoli into small florets, and trimming the snap peas.
Heat a large skillet or wok over medium-high heat and add a splash of oil. Once hot, add the marinated beef in a single layer. Cook for 2-3 minutes until browned, stirring occasionally.
Remove the beef from the skillet and set aside. In the same skillet, add the bell peppers, broccoli, and snap peas. Stir-fry for about 3-4 minutes until they are vibrant and slightly tender.
Return the beef to the skillet and combine with the veggies. Stir well and cook for an additional 2 minutes, allowing all the flavors to meld together.
Season with salt and pepper to taste. Remove from heat and garnish with chopped green onions and sesame seeds if desired.