1Slice the beef sirloin into thin strips.
Peel and slice the onion into thin wedges.
Cut the bell peppers into thin strips.
Mince the garlic cloves.
In a large skillet or wok, heat 1 tablespoon of olive oil over medium-high heat.
Add the beef strips and stir-fry until browned, about 3-4 minutes. Remove the beef from the skillet and set aside.
In the same skillet, add the remaining 1 tablespoon of olive oil.
Add the sliced onion, bell peppers, and minced garlic. Stir-fry for about 5 minutes until the vegetables are tender-crisp.
Return the beef to the skillet.
Add the soy sauce, chili paste, ginger, sesame oil, salt, black pepper, and red pepper flakes. Stir well to combine.
Cook for an additional 2-3 minutes until everything is heated through and well-coated with the sauce.
Serve hot and enjoy your Hot Chilli Beef Stir-Fry!