Preheat the oven to 350°F.
Coat the bottom of a 9-by-9-inch or similar-sized baking dish with a generous layer of olive oil (about 3 tablespoons). Squeeze the juice from the lemon into the dish.
Toss the artichoke bottoms with olive oil to coat and place open-side-up in a single layer in the prepared baking dish. Season with salt and pepper to taste.
In a medium bowl, combine the garlic, spinach, feta, mozzarella, nutmeg, and black pepper to taste.
Mound filling in each artichoke.
Bake covered for 15 minutes, then uncover and bake 15 more minutes until melty and lightly browned. Cool 5 minutes before serving.