Preheat oven to 425 degrees. On a large 13x9 baking sheet, roll out the pizza dough and stretch to fill the space. Set aside.
In a large skillet over medium heat, add the butter and allow to melt. Add the red onion and coat in the butter and allow to cook for 15-20 minutes, stirring occasionally, until the onions are soft, brown, and fully caramelized. Season with salt and pepper to taste, then transfer to a plate and set aside.
In the same skillet, add the ground beef and cook, crumbling, until browned, around 5 minutes.
Spread the BBQ sauce out over the pizza dough, stopping just before the edges. Distribute the caramelized onions and ground beef evenly over the dough, then sprinkle with the bacon pieces. Mix together the three cheeses and spread evenly over the pizza, then place in the oven and bake for 15-20 minutes, or until the cheese is bubbling and starting to brown. Remove from oven, allow to sit for a few minutes, then slice and serve.