Indian Spiced Tomato Soup with Cheesy Naan

Name: Indian Spiced Tomato Soup with Cheesy Naan
Ingredients: 5 tablespoons unsalted butter; 1 onion, chopped; 1/2 cup fresh cilantro leaves, plus 1 tablespoon chopped stems; 1 tablespoon plus 1 teaspoon minced garlic; 1 tablespoon minced fresh ginger; 1 teaspoon coriander seeds; 3 tablespoons tomato paste; 3 1/2 pounds plum tomatoes (about 20), cored and roughly chopped; Kosher salt and freshly ground pepper; 3/4 teaspoon garam masala; 1 8-ounce package naan bread; 1 8-ounce package shredded whole-milk mozzarella cheese