Soak twenty-four 15cm wooden or bamboo skewers in water for 30 minutes. Freeze the steak for 20 minutes.
To make the dipping sauce, mix together the vinegar, red capsicum, sugar, shallot, ginger, chilli-garlic sauce and lemon zest in a small serving bowl.
Blanch the capsicums in boiling water for 1 minute. Drain, rinse with cold water and pat dry with paper towels. Toss in a medium bowl with 2 tablespoons of the dipping sauce.
Preheat the grill to high. Slice the steak into 24 very thin strips, then thread a beef strip, a capsicum triangle and a piece of spring onion on to each skewer, twisting the meat round the vegetables. Grill for 3–5 minutes on each side or until cooked through. Serve the satay hot, with the rest of the dipping sauce.