Pre-heat the grill to hot.
Heat the olive oil in a large frying pan over a medium heat. Season the tofu slices and pan-fry for 5-7 minutes, turning occasionally, until golden brown in colour on the outsides.
Meanwhile, combine all the ingredients for the guacamole in mixing bowl and mash lightly until it comes together. Season to taste and set to one side.
Toast the burger bun halves until golden brown. Remove and spoon a tablespoon of the guacamole onto the bottom halves. Top with a slice of the tofu, then layer a slice of tomato on top. Follow with a little mixed leaf salad. Sit the top halves of the toasted burger buns on top and serve.