Step 1

Position a rack in the middle of the oven and preheat to 425 degrees.

Step 2

In a large skillet over medium heat, heat the oil until shimmering. Add the shallot or onion and cook, stirring frequently, until softened, about 1 minute. Add the spinach, a few handfuls at a time, and cook, stirring until all the spinach is wilted down, 4 to 5 minutes. Stir in the sun-dried tomatoes and remove from the heat. Stir in the Gournay cheese and pepper until well-combined. You should have about 1 cup of filling.

Step 3

Fill each mushroom cap generously with the spinach-cheese mixture (each cap should get about 1 tablespoon), piling the filling in a high mound. Place the mushrooms onto a large, rimmed baking sheet and sprinkle each with a little Parmesan cheese. Roast for 12 to 15 minutes, or until the mushrooms are tender and the cheese on top is nicely browned.

Step 4

Serve warm or at room temperature.