Preheat the oven to 425 degrees F (220 degrees C).

Combine ground chicken, bread crumbs, and soup mix in a large mixing bowl.

Place 4 ounces bacon in a food processor. Pulse 10 to 12 times and scrape down the sides. Combine the bacon with the ground chicken mixture; form into 6 patties and place on a baking sheet. Place in a freezer to chill for 12 minutes.

Bake patties in the preheated oven for 8 minutes. Reduce heat to 350 degrees F (175 degrees C) and continue cooking until browned, no longer pink, and an instant-read thermometer inserted into the center reads at least 165 degrees F (74 degrees C), about 12 minutes more.

Meanwhile, set a sauté pan over medium heat. Add butter and once butter is melted, add onion and mushrooms. Allow to soften, about 5 minutes. Sprinkle with salt and pepper.

Assemble chicken burgers by adding a chicken patty to each croissant, top with Swiss cheese, bacon, and the onion mushroom mixture. Serve immediately.