Set one oven rack/shelf about 4 inches from the broiler heat source. Preheat the oven broiler to high. Line a large, rimmed baking sheet with aluminum foil. Place a wire cooling rack on the aluminum foil, and spray the rack with nonstick cooking spray. Set aside.

Put half the mushrooms in the bowl of a food processor and pulse about 15 times, until the mushrooms are finely chopped but not puréed, similar to the texture of ground meat. Repeat with the remaining mushrooms. In a large skillet over medium-high heat, heat oil. Add the mushrooms and cook for 2 to 3 minutes, stirring occasionally, until the mushrooms have cooked down and some of their liquid has evaporated. Remove from the heat.

In a large bowl, combine the pork with the cooked mushrooms, oregano, fennel, pepper and salt. Mix gently using your hands. Form the meat into 6 small (1/2-inch-thick) sausage patties, and place on the prepared rack, making a line of patties down the center of the pan.

Place the pan in the oven so the broiler heating element is directly over as many patties as possible. Broil for 4 minutes. Flip the patties and rearrange them so any patties not getting brown are nearer to the heat source. Broil for 3 to 4 more minutes, or until the internal temperature of the meat is 160°F on a meat thermometer. Watch carefully to prevent burning.