Heat oil in a large pot on medium-high heat and add onion. Cook until softened, about 4 minutes, then stir in garlic and cumin. Continue to cook until onion begins to brown.
Stir in tomatoes and coconut and the coriander, salt, turmeric, cayenne pepper, cinnamon, ginger, and cardamom. Stir until mixture begins to boil, then put in the potatoes, cauliflower, and garbanzo beans. Blend well. Reduce heat to low and cover.
Simmer until the potatoes are tender, 45 minutes to an hour (this will depend on the size of the potato chunks). Sprinkle in the garam masala, stir, and cook for an additional 5 minutes.
