Pour olive oil into a large mixing bowl. Add Knorr Beef Stock pot, crushed garlic and lime juice. Stir well until ingredients are evenly mixed.
Remove fat from sirloin steak, slice into 3-5 mm thick strips. Add sirloin strips to marinade and rub the marinade into the meat by hand. Transfer the entire content into plastic bag and marinate in fridge or 30 minutes (or for great result marinade overnight).
Remove steak from marinade (discarding the marinade) and grill for 3-8 minutes depending on how you like your steak cooked.
Warm the tortillas under the grill for 2 minutes, lay onto flat plates and spread each with 1 tablespoon mayonnaise. Add half of the steak strips to each.
Garnish with toppings of your choice, such as strips of mature Cheddar cheese, shredded lettuce, chopped tomatoes and sour cream. Serve with wedges of lime.