Spinach-Artichoke Grilled Cheese

Name: Spinach-Artichoke Grilled Cheese
Prep time: 30 min
Cook time: 14 min
Total time: 44 min
Cuisine: American, Mediterranean
Ingredients: 1 (10-ounce) package frozen chopped spinach; 4 ounces cream cheese; 2 ounces Parmesan cheese (heaping 1/2 cup store-bought grated); 2 medium scallions; 1 (6.5-ounce) jar marinated artichoke hearts; 1 medium lemon; 1 teaspoon garlic powder; 1/2 teaspoon kosher salt, plus more as needed; 1/2 teaspoon freshly ground black pepper; 4 to 8 slices provolone cheese, divided; 4 tablespoons mayonnaise, divided; 8 slices sourdough sandwich bread