In a bowl combine the oil, lime juice, garlic, lime zest, chilli, salt and pepper. Place half of the mixture in a ceramic dish with the beef cover and refrigerate for 4-8 hours; turning hourly. Refrigerate remaining marinade.
Drain meat and discard marinade. In a cast iron or heavy frying pan heat 2 tablespoons (40 ml) olive oil over high heat. Once hot add beef, red capsicum and red onion; stir and brown slightly.
Add the reserved marinade and reduce heat to medium. Cook and stir until beef reaches desired doneness and vegetables are tender but still slightly crisp.
Add the spring onions and fresh coriander; stir and remove from heat.
Meanwhile; heat the flour tortillas in a microwave on high for 20 seconds.
Serve the fajitas by bringing the frying pan to the table with the tortillas and desired accompaniments. Let each person assemble their own fajitas.