Preheat the oven to 375°F and coat a shallow baking sheet with nonstick spray.
Arrange the mushroom caps on the prepared sheet and sprinkle with salt and pepper.
Heat the olive oil in a skillet over medium heat. Add the garlic and sauté until fragrant, 1 to 1-1/2 minutes
Remove the garlic with a slotted spoon, then return the pan to the stove over medium-high heat.
Add the spinach and sauté until wilted, tossing constantly with tongs, 2 minutes.
Season lightly with salt and pepper, remove the pan from the heat and drain any liquid that may have accumulated.
Stir in the sun-dried tomatoes and set aside to cool for about 5 minutes.
Using a small spoon (or your fingers), fill the mushroom caps with the spinach mixture, then top with each with cheese.
Bake for 10 to 12 minutes, or until the mushrooms are tender and the cheese is bubbly and lightly browned.
Tips for Making This Recipe
Make-Ahead Instructions
To prepare this recipe in advance, follow the recipe, but omit the cheese before baking and let the mushrooms to cool completely before storing in the refrigerator.When you're ready to serve, bring the mushrooms to room temperature for about 30 minutes, then top with the cheese.Bake at 400°F until the cheese is melted and the mushrooms are heated through, 5 to 7 minutes. Serve immediately.