"This crazy flavorful burger gets some good-for-you brownie points for including roasted mushrooms and sauteed kale, a tribute to the Blended Burger Project™. This initiative is part of a nationwide effort, spearheaded by the James Beard Foundation, to lighten up burgers without sacrificing juiciness or taste."
Place mushrooms in a food processor; pulse until finely chopped. Transfer to a roasting pan. Drizzle 2 tablespoons olive oil on top and mix. Sprinkle with salt.
Bake in the preheated oven until tender, about 10 minutes. Cool to room temperature, about 15 minutes.
Heat remaining 1 tablespoon olive oil in a large skillet over medium heat. Add kale; cook and stir until just wilted, 2 to 4 minutes. Let cool slightly, about 5 minutes.
Transfer kale to the food processor; pulse until finely chopped.
Combine mushrooms, kale, Italian sausage, and harissa in a bowl; mix together by hand. Form into 4 patties, taking care not to pack them too firmly.
Heat an oven-safe grill pan or cast iron skillet over medium-high heat. Add patties; cook until browned, about 5 minutes. Flip.
Transfer grill pan to the oven and continue cooking until second side is browned, about 8 minutes. Place a slice of mozzarella cheese on top of each patty and broil until cheese melts, about 1 minute.
Serve patties on toasted buns with marinara sauce.