Combine Neufchâtel, half the beans, lemon juice, half the Parmigiano Reggiano, rosemary, garlic, and milk in a food processor, and purée until smooth. Taste, and add salt and pepper if desired. Set aside.
Heat oven to 500°F. Heat olive oil in skillet over medium heat. Sauté leek slices 4 minutes, or until tender. Add spinach and cook 3 minutes, or until spinach wilts. Set aside.
Dust a baking sheet with flour. Stretch dough into a 13-by-9-inch rectangle, and transfer to baking sheet, rolling sides of dough inward to create a 1-inch-wide crust.
Top dough with white bean sauce, leek and spinach mixture, artichoke hearts, remaining beans, green onions, mozzarella, remaining Parmigiano, and red pepper flakes.
Bake 10 to 15 minutes, or until bottom of crust is crisp and brown. Transfer to a cutting board. Let cool 5 minutes before serving.