Wipe the mushroom tops with a damp paper towel to remove any debris, avoiding a full wash which makes them soggy. Remove the stems by hand and choose whether to scrape out the gills for a cleaner look or leave them for a deeper, earthy flavor.
Whisk together the olive oil, balsamic vinegar, soy sauce, and Dijon mustard in a small bowl. Stir in the minced garlic, smoked paprika, and black pepper to create a thick, savory marinade that mimics the “umami” profile of a traditional steak.
Place the mushroom caps in a shallow dish and coat them thoroughly with the marinade. Let them sit at room temperature for at least fifteen minutes, turning them halfway through to ensure every crevice absorbs the liquid.
Bring a cast-iron skillet or grill pan to medium-high heat until a tiny bit of smoke rises from the surface. Lightly oil the pan to prevent sticking and ensure a dark, professional sear on the mushroom skins.
Place the mushrooms cap-side down and press them firmly with a heavy spatula to maximize contact with the heat. Sear for four to five minutes until the exterior is deeply browned and caramelized, then flip them to the gill side.
Pour any remaining marinade over the mushrooms as they finish cooking for another four minutes. Once the “steaks” are tender but firm, move them to a plate to rest for three minutes, allowing the juices to settle before serving with fresh parsley.
