How to Make It
In a skillet, cook the bacon over moderate heat, stirring until cooked through, about 3 minutes. Transfer the bacon to paper towels to drain and let cool. In a large bowl, mix the bacon with the ground pork, garlic, thyme, salt and pepper. Shape into four 1-inch-thick patties.
Light a grill. Drizzle the onion slices with olive oil and grill over moderately high heat until lightly charred, about 2 minutes per side. Transfer to a platter. Brush the cut sides of the buns with the melted butter and grill, cut sides down, until toasted, about 1 minute. Turn and grill for 30 seconds longer. Transfer the buns to the platter.
Grill the burgers until charred outside and cooked through, about 5 minutes per side. Arrange 2 Camembert slices and a Gorgonzola slice on each burger and cook until the cheese is melted, 1 minute.
On the bottom halves of the buns, layer the arugula, tomato, burgers and grilled onion. Close the burgers and serve.