In a large mixing bowl gently mix together the pork, bacon, Dijon, crushed red pepper, salt and pepper with your hands until just combined. Form 4 equal patties, slightly larger than the burger buns.
Heat a large cast iron pan over medium-high heat. Working 2 patties at a time, add to the pan and cook until a browned crust forms, about 4 minutes. Flip and continue to sear until cooked through, about an additional 4 minutes. Remove from the pan and set aside on a plate. Repeat with the remaining patties.
For the beer cheese:
Add the cheese, cream cheese, garlic and Worcestershire to the bowl of a food processor fitted with the blade. Pulse until the cheese is finely chopped.
Slowly pour the beer in and pulse the food processor until a fondue-like texture is achieved. Add to a bowl, cover with plastic wrap and refrigerate for an hour.
For assembly:
Heat oven to broil.
Heat a large sauté pan over medium heat, add the oil and heat through. Add the onions and sauté, stirring occasionally until they begin to brown slightly, about 8 minutes. Remove from heat and set aside.
Arrange the pretzel buns on a baking sheet and broil until golden brown. Spread a generous amount of the beer cheese on the top bun and mustard on the bottom bun.
Add the a patty on top of each of the bottom buns, top with onions and arugula then close with the top bun spread with the beer cheese. Serve immediately.