In a bowl combine the chicken with the garlic, cumin, chilli, paprika, oregano, orange rind and juice, lemon juice, 1 tablespoon oil and 3 tablespoons coriander. Mix well so that all the chicken strips are coated, then leave to marinate for at least 15 minutes, or while you prepare the rest of the dish.
For the salsa, combine all the ingredients. Add the remaining chopped coriander and mix.
Preheat the oven to 180 degrees C. Heat a heavy-based frying pan until very hot. Brush with the remaining oil. Add the green capsicums and onions and cook for 6–8 minutes or until tender and lightly charred (do this in batches, if necessary). Remove from the pan and set aside.
Wrap the tortillas, stacked up, in foil and place in the oven to warm for 10 minutes. Meanwhile, preheat the grill to high. Spread out the chicken in a shallow layer in the grill pan. Grill close to the heat, turning once or twice, for about 5 minutes or until thoroughly cooked.
To serve, divide the chicken, onions and capsicum among the warm tortillas and roll up. Garnish with sprigs of coriander and serve with the salsa and sour cream. Or present the ingredients separately, with the tortillas wrapped in a cloth to keep them warm, and let your guests make their own fajitas.