Prep the mushrooms: Heat the oven to 375°F (190°C). Wipe mushrooms clean with a damp paper towel. Twist out the stems and finely chop them. Toss mushroom caps with 1 tablespoon olive oil, a pinch of salt, and black pepper. Set aside.

Brown the sausage: In a large skillet over medium heat, add the sausage. Cook, breaking it up, until browned and cooked through, 6–8 minutes. Drain excess fat if needed, leaving about 1 tablespoon in the pan.

Sauté aromatics: Add the remaining 1 tablespoon olive oil if the pan looks dry. Stir in onion and chopped mushroom stems. Cook until softened and most moisture cooks off, 4–6 minutes. Add garlic and cook 30 seconds until fragrant.

Build the filling: Reduce heat to low. Stir in cream cheese until melted and smooth. Remove from heat and fold in Parmesan, parsley, red pepper flakes, salt, and pepper. Taste and adjust seasoning. If you want crunch, fold in half the panko.

Stuff the caps: Arrange mushroom caps, cavity side up, on a parchment-lined baking sheet. Spoon the sausage mixture generously into each cap, mounding slightly.

Top and bake: Sprinkle with a little extra Parmesan and the remaining panko. Bake 18–22 minutes, until the tops are golden and the mushrooms are tender but still hold their shape.

Finish and serve: Let cool 5 minutes. Add a light squeeze of lemon over the top for brightness. Serve warm with extra parsley if you like.