In a small bowl, combine all the sauce ingredient together and set aside.
In another small bowl combine thinly sliced beef steak with all the beef marinade ingredients together. Cover and refrigerate for 30 minutes.
Add the egg whites to the beef mixture and mix it well. Add the cornstarch to a large shallow dish then dredge the beef strips through the cornstarch, making sure they're fully coated.
Heat 1 inch of vegetable oil in a large wok over medium-high heat until it reaches about 350°F. Add the beef to the wok and cook for 2 to 3 minutes, until crispy. Transfer the beef to a plate lined with paper towels to drain excess oil.
Remove the oil and add the 2 tablespoons of grapeseed oil to the wok and heat over medium heat. Add the garlic and cook for 30 seconds until aromatic. Add the onion and bell pepper and cook for another 1 to 2 minutes.
Pour in the sauce, stir and cook until the sauce thickens. Return the crispy beef to the wok, tossing to coat evenly with the sauce.
Garnish with chopped green onions and sesame seeds before serving.
