Heat the oil in a large deep ovenproof frying pan over high heat and fry the onion until soft. Then add the peppers and mushrooms and cook for a few minutes until golden and soft.
Add beef, stirring with a wooden spoon to break up any lumps, for 3 - 5 minutes or until browned.
Stir in garlic, chilli and taco seasoning. Stir in chopped tomatoes, beans, sweetcorn kernels and stock. Cook, stirring, for 3 - 5 minutes or until thickened slightly.
Meanwhile, preheat the grill to high.
Sprinkle with Mexican beef with cheese and place under the grill for 2 - 3 minutes or until the cheese is golden.
Top with coriander, feta and chopped tomato.
Season and serve with a side salad and lime wedges.