Heat oil in a non-stick frying pan and crumble in the mince meat and chopped onion. Cook for 15 minutes, stirring so it browns all over.
Blend the contents of the sachet with water and add to the mince, with the pre-prepared lentils. Cook for another 5 minutes until the lentils are soft and beef is cooked through.
Prepare the tortillas by toasting them in a hot, dry frying pan, or over a flame until lightly blistered.
To serve, lay the toppings and mince on the table for everyone to assemble as they like!
Add the lime wedges on the side for squeezing over.