Preheat the oven to 450°
Brush the insides of the mushroom caps with the oil and season 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 and mayonnaise 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 1 Tbsp of oil, 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. Serve immediately.