Add 3 Tbsp or so vegetable oil to a large non-stick frying pan over medium heat. When oil is warm, add cinnamon, cardamom, and cloves. Stir fry for about 30 seconds.
Add the onions and optional green chilies. Fry until the onions are lightly golden brown, about 5 minutes. Stir frequently. Add ginger and garlic paste, stir for a couple minutes longer. Add tumeric, red chili owder, coriander, and garam masala. Fry for 5 minutes over low heat.
Add the tomatoes, cumin, tomato paste, and 1 cup hot water. Stir until the water is absorbed. Turn the heat to low, cover, and simmer for 10-15 minutes or until the oil separates and rises to the top.
Turn the heat to high and add the shrimp and 2 pinches salt. Add another cup of warm water to the pan.
Add 1 cup warm water to the pan. When simmering, cover and turn the heat back down to low. Let cook 10 minutes or unti the prawns are done. Garnish with coriander leaves.