Heat oil in a stock pot over medium heat. Add garlic and ginger; cook until fragrant, about 2 minutes. Add chicken pieces, tomatoes, salt, and red pepper flakes. Cover and cook over high heat, stirring every 5 minutes, until mixture has thickened, about 20 minutes. Add green chiles and water; cook and stir, uncovered, until water mostly evaporates, about 15 minutes more. Top with cilantro leaves.
