Heat oil in a frypan on medium-high heat. Cook beef, stirring, for 5 minutes, until browned. While beef cooks, dice onion. Add onion and cook for about 5 minutes, until softened. Add measure of spices and tomato sauce and cook a further 1 minute, until combined. Season with salt and pepper. Set beef aside, wipe pan clean and reserve.
Grate cheese and shred lettuce.
Spread burger sauce on tortillas then fill with beef, cheese and lettuce (or keep lettuce until after frying) and cheese. Fold each tortilla in half.
Heat oil in reserved frypan on medium-high heat. Cook tortillas, in batches if needed for 1-2 minutes each side, until golden and cheese is melted.