Combine the first 4 ingredients in a bowl. Divide and spread on one side of each tortilla. Divide and lay the beef on top of mayonnaise mixture. Divide and make rows of the avocado and lettuce down the centre of each tortilla. Fold over the sides of the tortillas and then tightly roll into closed cylinders. Slice each tortilla in half at a slight angle, if desired.
Note: To make tortillas easier to roll, heat 15 to 20 seconds in the microwave before using.