An Oktoberfest take on the burger: Sweet Italian sausage and mushrooms in a patty. Dress the ciabatta roll with mayo, add a patty, some Provolone, and that all important broccoli rabe.
Heat 1 tablespoon oil in a large nonstick skillet over medium-high. Add mushrooms; season with salt. Cook, stirring occasionally, until golden brown, about 5 minutes. Transfer to a bowl. Heat 1 more tablespoon oil in skillet over medium-high. Add broccoli rabe; season with salt. Cook until crisp-tender, about 4 minutes. Stir in lemon juice and red-pepper flakes. Transfer to another bowl.
Wipe skillet clean. Stir together sausage and mushrooms; season with salt and pepper. Form into 4 patties. Heat remaining 1 tablespoon oil in skillet over medium-high. Cook patties, flipping once, until just cooked through, about 6 minutes. Top each with cheese, cover, and cook until melted, about 30 seconds. Serve on rolls with mayonnaise, broccoli rabe, and more red-pepper flakes.