In a large skillet cook ground beef over medium-high heat until browned. Drain off fat. Stir in salt and pepper.
Line a 6-qt. oval slow cooker with parchment paper, then foil. Coat foil with cooking spray. On a lightly floured surface, roll dough into a 14x11-inch oval. Transfer to paper-foil liner in cooker. Fold down top edges of dough to make an even crust that extends 1 to 1 1/2 inches up the sides.
Spread ketchup and mustard over bottom of crust. Top with meat, half of the cheddar and mozzarella cheeses, the onion, and pickles.
Cover and cook on high 3 1/2 hours or until crust is golden, giving crockery liner a half-turn halfway through if possible. Sprinkle with remaining cheeses. Cover and cook 10 minutes more. Turn off cooker. If possible, remove crockery liner from cooker. Let stand, uncovered, 15 minutes before serving. Top with bacon.