Brown the mince in a little oil a frying pan
Add the onions, garlic and peppers and cook through til the onions are transparent
Add the tomatoes and fajita seasoning and let it bubble. If it's a little dry, add some water
Either cover the pan, turn down the heat and simmer for 45 minutes on the hob. Alternatively, cover and simmer in the bottom of the oven at around 150C or simmer in a slow cook on low for however long your slow cooker needs.
If not using ready-made cheese sauce, make the sauce. Mine's an easy microwave cheese sauce)
Once the mince is cooked, layer up the lasagne. Start with mince, then tortilla, then cheese sauce, repeat until finishing with cheese sauce.
Top with the broken tortilla crisps if using, then the grated cheese
Bake in the oven at around 200C until the cheese on top melts
Serve with spring onions sprinkled on top, and with dollops of guacamole and source cream on the side.