Position a rack in the center of the oven and preheat the oven to 350 F.
Lightly oil a baking dish that holds about 6 cups.
Heat the oil in a separate small skillet over medium heat.
Add the onion and cook, stirring often, until softened, about 3 minutes.
Stir in the garlic and cook until fragrant, about 1 minute more.
Transfer to a medium bowl and cool slightly.
Add the cream cheese and mayo to the bowl and using a spatula, mash them together to combine.
Add the Parmesan cheese (3/4 cup) and hot pepper sauce and mix well.
Squeeze the excess liquid from the spinach, and then add to the cream cheese mixture.
Add the artichoke hearts and mix well.
Spread in the baking dish and sprinkle with the remaining Parmesan (at this point, the dip can be covered with plastic wrap and refrigerated for up to 24 hours.)
Bake until the dip is bubbling and browned, about 35 minutes.
Serve with toasted baguette slices (brushed with olive oil and sprinkled with a little oregano before toasting under the broiler).