Arrange tomatoes, cut sides down, on a foil-lined baking sheet. Cut chiles in half lengthwise; discard seeds and membranes. Place chiles, skin sides up, on baking sheet; flatten with hand. Broil 15 minutes or until blackened. Remove from oven; let stand 15 minutes. Peel tomatoes and chiles; place in a small bowl. Place onion and garlic on baking sheet; lightly coat with cooking spray. Broil 20 minutes or until browned, turning after 10 minutes. Add onion and garlic to tomatoes in bowl. Discard foil.
Arrange tortilla strips in a single layer on a baking sheet; coat with cooking spray. Broil 9 minutes or until lightly browned, stirring occasionally.
Place tomatoes, chiles, onion, and garlic in a food processor. Process 1 minute or until blended. Spoon tomato mixture into a large saucepan; cook over medium heat 2 minutes, stirring constantly. Reduce heat to low; cook 6 minutes, stirring occasionally. Stir in cilantro and the next 5 ingredients (through broth); bring to a boil. Cover, reduce heat, and simmer for 15 minutes. Ladle 1 cup soup into each of 8 bowls; top each serving with about 6 tortilla strips, 1 tablespoon avocado, 1 tablespoon queso fresco, and 1 cilantro sprig.