3 tablespoons olive oil
3 medium cloves garlic, minced (1 tablespoon)
4 medium portabello mushrooms, stemmed, gills removed
Freshly ground black pepper
4 oz. cream cheese, softened
3 tablespoons mayonnaise
1-1/2 teaspoons fresh thyme
9 to 10 oz. frozen chopped spinach, thawed and squeezed dry
9 oz. frozen artichokes, thawed, lightly squeezed dry, and chopped
1/2 cup fresh breadcrumbs or panko
1/3 cup finely grated Parmigiano-Reggiano
Position a rack in the center of the oven and heat the oven to 450°F.
In a small bowl, combine 2 tablespoons of the oil and about 2/3 of the minced garlic. Brush the insides of the mushroom caps with the garlic oil and sprinkle generously with salt and pepper. Arrange the mushrooms oiled side up on a rimmed baking sheet and roast until just tender, about 10 minutes.
Meanwhile, in a medium bowl, mix the cream cheese, mayonnaise, and 1/2 teaspoon of the thyme with the back of a wooden spoon. Stir in the spinach and artichokes and season to taste with salt and pepper. In another medium bowl, combine the remaining garlic, 1 tablespoon oil, and 1 teaspoon thyme with the breadcrumbs and cheese.
Spoon the artichoke mixture evenly into the mushroom caps and sprinkle with the breadcrumb mixture. Bake until the crumbs are golden-brown and the filling is hot, about 10 minutes.