Place the breadcrumbs, chicken and chopped bacon into a mixing bowl. Grate the lemon zest in with the chicken and bacon, then halve and squeeze the lemon. Add the lemon juice to the mixture with the roughly chopped thyme leaves. Tip in the grated parmesan. Season the mixture with a little salt, then more generously with black pepper. Mix thoroughly.
Shape the mixture into small balls or patties. Warm the olive oil in a non-stick pan. Fry them in the oil, about eight at a time, for 4-5 minutes until they are crisp and golden-brown on all sides. Lower the heat and leave to cook through to the middle, about 6-8 minutes more. I tend to turn them no more than once or twice during cooking so they develop a crisp, slightly sticky exterior.
Remove the cakes from the pan and place on large, crisp lettuce leaves, add a dollop of mayonnaise and wrap the cakes in the leaves.