To start with, cut the beef fillet into thin strips.

Heat oil in a wok and fry beef strips over high heat until lighly browned. Set aside.

Meanwhile dice capsicum and onions. Then slice garlic, ginger, and green chillies. (I've used both green and red chillies here. I've also removed the seeds to make them less spicy)

Heat more oil in the same pan over low heat, and fry garlic first, and then ginger until lightly browned.

Now add in the diced onions, and cook, stirring, for 2-3 minutes or until softened. Throw in the green chillies and fry again.

Add capsicum and fry again. Return the fried beef strips to the pan and mix well. Stir in soy sauce and sweet chilli sauce. Sprinkle with ground black pepper and crushed beef stock cube. Give it a good stir. Turn up the heat again, and fry, stirring continuously, for 2-3 minutes.

To serve, place the chilli beef in a serving bowl, and garnish with sliced spring onions.