Mix together beef strips, cornstarch, pineapple juice, soy sauce, salt, and pepper together. Marinate for 15 minutes.
Cook the beef
Using a wok, heat up 1 tbsp of oil. Add in sliced onions and cook for 2-3 minutes until fragrant. Add in the beef mixture. Cook for 4-5 minutes until the beef is just about cooked through- medium rare. Remove from the pan and set aside.
Remove lid, add back in your beef. In a separate small bowl, mix together corn starch, soy sauce, and brown sugar- add this mixture into the wok. Carefully mix together.
Garnish with scallion and sesame seeds, enjoy!
Notes
Notes: You can substitute beef with firm tofu, chicken, turkey breast.