Cut the avocados in half, scoop out the stone, peel away the skin and cut the flesh into small chunks. Divide the avocado between the wraps and using a fork, mash the flesh onto the wraps to cover – just like a thick layer of butter. Sprinkle lemon juice over the top.
Put the tuna and beans into a small bowl, add the mayonnaise, mint or coriander and freshly ground black pepper. Mix together.
Scatter the tuna and beans over the avocado and then roll each wrap up as tightly as possible. Cut into pieces and pack into a picnic container ready to take along.