Cook the onions and oil in a large skillet until slightly browned then add in the uncooked meat and cook through, stirring occasionally then drain.
Mix in the mustard, ketchup and diced dill pickles and simmer for 3 minutes over low heat stirring occasionally.
Turn off the heat and stir in half of the cheese.
Now, lay the tortillas out flat and scoop the meat mixture into each one. Then top with the rest of the cheese, chopped tomatoes and lettuce.
Fold in the ends and roll up the tortillas.