Heat the oil in a large pot over medium heat. Add the diced onion and cook for 5–7 minutes until softened and translucent. Add the minced garlic, cumin, and curry powder. Cook for 1 minute, stirring constantly, until the spices are fragrant.
Pour in the diced tomatoes (with juices), chickpeas, and water (or stock). Stir to combine and bring the mixture to a boil.
Reduce the heat to medium-low and let it simmer uncovered for 15 minutes. The liquid should reduce slightly, and the chickpeas will soften.
Remove the pot from the heat (this is crucial to prevent curdling). Let it sit for 2 minutes to cool slightly, then whisk in the Greek yogurt until the sauce is smooth and creamy.
Taste and season with salt. Serve warm over rice or with toasted naan.