In a bowl, mix pork, bacon, Dijon, thyme, red pepper, salt, and pepper. Form 4 patties.
Heat cast iron skillet over medium-high, cook patties 4 minutes per side until browned and cooked through.
In food processor, pulse cheeses, cream cheese, garlic, and Worcestershire. Slowly add beer until smooth. Chill 1 hour.
In pan, sauté onions until golden, about 8 minutes.
Broil pretzel buns until golden. Spread beer cheese on tops, mustard on bottoms.
Assemble burgers with patties, onions, arugula, and beer cheese tops. Serve immediately.
