"These burgers are bursting with flavor! Seasoned meat stuffed with fontina and bacon topped with Gorgonzola and a red Zinfandel mushroom sauce! Make sure you're hungry, these burgers are very filling!"
Preheat an outdoor grill for medium-high heat, and lightly oil the grate.
Mix together the ground beef, onion soup mix, 1 cup minced red onion, Worcestershire sauce, garlic, and Dijon mustard with your hands. Shape the mixture into 4 patties of equal size. Place about half of the fontina cheese and bacon bits in the center of 2 of the patties; top with the other 2 patties and press edges of the patties to seal the cheese and bacon inside.
Heat the olive oil in a large skillet over medium-high heat. Cook 1 cup red onion in the hot oil until translucent, about 5 minutes. Add the mushrooms and garlic to the onions; cook and stir until the mushrooms are softened, about 5 minutes. Pour the beef broth and Zinfandel into the skillet and bring to a simmer; allow to cook until the liquid reduces by about half.
Cook burgers on the preheated grill to your desired degree of doneness, 7 to 10 minutes per side for well done. An instant-read thermometer inserted into the center should read 160 degrees F (70 degrees C). Top the burgers with equal amounts of the Gorgonzola cheese; cook until the Gorgonzola begins to melt, about 1 minute more. Place the burgers on the Kaiser rolls and top with the Zinfandel reduction sauce to serve.