Giant Spinach Dip-Stuffed Pretzel

Nonstick cooking spray, for the baking sheet

marinated artichoke hearts, drained

box frozen spinach, thawed

cream cheese, at room temperature 

grated Parmesan

garlic powder

Kosher salt and freshly ground pepper

tubes refrigerated pizza dough

part-skim mozzarella string cheese

baking soda

unsalted butter, melted

Pretzel salt or other coarse salt, for topping