Preheat oven to 400 degrees F.
Coat a rimmed 12 by 16-inch cookie sheet with non-stick spray. Stretch bread dough into cookie sheet. Cover with plastic wrap and let rest for 10 minutes. Continue to stretch dough so it fills the pan, and form a ridge around edge, making a crust. Bake 15 to 20 minutes or until golden brown, and let cool.
Spread mustard onto the pre-baked tart. Top with sauerkraut, prosciutto and bits of cheese. Bake 10 minutes, or until cheese is melted.
Let cool for 5 to 10 minutes, then cut into squares and serve.