Preheat a griddle to 350ºF.
Combine the mayonnaise and vinegar in a small bowl. Spread 1 tablespoon on each cut side of the focaccia.
Add a little oil to the griddle. Place the focaccia, mayonnaise side up, on the griddle. Put 2 slices of cheese on top of each piece of bread, and cover with a heatproof bowl to melt the cheese.
Meanwhile, divide the turkey into 2 portions and put on the griddle to warm. Place the bacon slices in an “X” over each portion, and cover with the avocado and remaining cheese. Once the cheese is melted all around, put a mound of turkey on 2 bottom halves, and top with the remaining bread.