Heat oil in a 4-quart pot over medium heat. Add onion and garlic; cook, stirring occasionally, until onion is softened and golden, about 8 minutes. Add ginger, chopped chiles, and spices; cook, stirring occasionally, until fragrant, about 2 minutes.
Stir tomatoes and their juice, beans and their liquid, and salt. Bring to a boil, reduce heat, and simmer until thickened slightly, about 10 minutes.
Coarsely mash a third of the beans in a pot using a potato masher or an immersion blender; stir to blend into soup.
Top with yogurt,cilantro sprigs, and sliced chiles, and serve with pita chips.