In a food processor add tomato, garlic, ginger, and jalapeno. Pulse them until pureed.
Heat oil in a medium-size skillet over medium heat. Add onion and cook until it turns golden brown.
Add the tomato-garlic puree and tomato paste, and cook for about 5-6 minutes or until much of the water evaporates.
Add coconut milk, garam masala, salt, and ½ cup water. Bring the mixture to a boil. Add remaining water, if necessary.
Add cleaned shrimp or prawns and cook for 2-3 min on each side or until well done.
In the end, sprinkle some chopped cilantro and serve warm.