This is as close as I’ve ever gotten to a delicious non-meat burger. Mushrooms really give this a meaty flavor. I serve this like I serve a regular burger, on a nice fresh hamburger roll with spicy mayonnaise and a little lettuce.
Heat 2 tablespoons olive oil in a large skillet over medium heat; add mushrooms, onion, and garlic to the hot oil and season with salt, black pepper, and oregano. Cook and stir mushroom mixture until mushrooms have given up their juice and the juice has almost evaporated, about 10 minutes. Transfer cooked mushrooms to a cutting board and chop into small chunks with a knife.
Transfer mushrooms to a large bowl. Mix in rolled oats and bread crumbs; taste for salt and black pepper and add more to taste. Stir Parmigiano-Reggiano cheese into the mixture, followed by eggs. Let mixture stand for the crumbs to soak up excess liquid, about 15 minutes. (At this point you can refrigerate the mixture to cook later if desired.) Moisten hands with a little vegetable oil or water, pick up about 1/4 cup of mixture, and form into burgers.
Heat remaining 2 tablespoons olive oil in a skillet over medium heat and pan-fry burgers until browned and cooked through, 5 to 6 minutes.
Per Serving: 255 calories; protein 11.4g; carbohydrates 22.5g; fat 14.2g; cholesterol 66.8mg; sodium 630.3mg.