In a small bowl, add soy sauce, mirin, brown sugar, sesame oil & fish sauce. Stir to mix through. Set aside
In a large bowl add 1/2 cup corn flour & beef strips. Toss to coat the beef strips in the corn flour.
Heat 2 tbsp peanut oil in a wok over medium high heat.
Add beef strips and cook for about 4-5 minutes or until browned. Note: cook beef in two batches for a better result. Remove from wok, set aside & keep warm.
Add 2 tbsp peanut oil to wok.
Add garlic & ground ginger and cook for about 30 seconds.
Reduce heat then add red capsicum, broccoli & soy sauce mixture to wok and simmer for 2-3 minutes.
Add 1 tsp corn flour & 1 tbsp water in a small bowl and stir to mix.
Add corn flour mixture to wok and stir to mix through.
Add beef strips to wok, stir to coat with teriyaki sauce and cook for a further 2 minutes. Stir regularly.
Remove from heat, garnish with spring onion and serve with rice.