Preheat oven to 450°.
Place eggplant, cut sides down, in a baking pan coated with cooking spray; add garlic. Bake at 450° for 30 minutes or until eggplant is tender; cool. Scrape pulp from eggplant skins; discard skins. Squeeze cloves to extract garlic pulp; discard skins.
Place coriander and cumin in a spice or coffee grinder; process until finely ground. Heat oil in a medium saucepan over medium heat. Add spice mixture, onion, and pepper; cook 5 minutes or until onion is tender, stirring frequently. Add flour; cook 2 minutes, stirring constantly. Add water and vegetable broth, scraping pan to loosen browned bits. Cool 5 minutes.
Combine eggplant pulp, garlic pulp, and broth mixture in a blender, and process until smooth. Return the pureed mixture to pan. Bring to a simmer over medium-high heat, and cook 3 minutes, stirring frequently. Stir in balsamic vinegar. Ladle 1 1/2 cups soup into each of 2 bowls. Top each serving with 1 tablespoon yogurt and 1 teaspoon cilantro.