Preheat the oven to 180°C/350°F/Gas mark 4.
In a non-stick frying pan, heat the oil over a medium-high heat. Cook the onion, garlic, chilli powder and seasoning, stirring, for 5 minutes or until the onion is softened.
Add the beef and salsa, and cook, breaking up the beef with the back of a spoon, for about 3 minutes until the beef is no longer pink. Add the peppers and courgette, and cook, stirring, for 3 minutes or until the liquid has evaporated.
Meanwhile, wrap the tortillas in foil and heat in the oven for 5 minutes or until warmed through.
Divide the beef mixture among the tortillas, and roll up. Serve the fajitas immediately while still piping hot.