Heat a 10-inch saute pan over high heat. When hot add the olive oil, onions, and season with some salt and black pepper. Reduce heat to medium-high and continue to cook for 10 minutes until caramelized, stirring often. Sprinkle in the thyme and continue to cook for one minute. Add the Zinfandel and cook until wine is 2/3 reduced. Take off the heat and let cool to room temperature.
For the Cheddar fricos: In an 8-inch nonstick pan heated over medium-high heat add 1/4 cup shredded cheese. Cook until cheese is light brown on the bottom. Turn over with a plastic spatula and continue cooking for another 10 to 15 seconds. Remove to a plate to cool. Wipe pan and start again until 6 fricos are complete.
Form 6 (1/2-pound) beef patties and season very well with sea salt and black pepper on each side. Place on a hot grill and cook until nicely browned, approximately 5 minutes. Turn over and continue to cook to desired doneness.
A couple of minutes before the burgers are done halve the rolls and lightly brown on the grill, open side down.
Place burgers on the bottom halves of the rolls, adding a generous helping of onions. Season the tomato slices with salt and pepper. Top the burgers with frico, tomato slice and greens. Roll up your sleeves and dive in.