In a 6- to 8-qt. pot, cook onion in oil over medium heat until softened, about 10 minutes. Add garlic and cook 2 minutes. Add ginger and spices and cook until fragrant, about 1 minute. Working in batches, stir in spinach and cook until wilted, about 5 minutes. Remove from heat and stir in yogurt and salt. Serve with steamed basmati rice and warm naan (Indian flatbread).
Note: Nutritional analysis is per 1 1/2-cup serving.