Heat oil in a large skillet over medium heat. Add onion, jalapeno, and 3/4 teaspoon salt. Cook, stirring occasionally, until onion begins to soften, 3 to 5 minutes. Add tomato paste, curry powder, and ginger. Cook, stirring to break up paste, until mixture is smooth and fragrant, about 1 minute.
Add tomatoes to skillet. Cook, stirring, until they begin to release their juices, about 1 minute. Add 1 1/2 cups water; simmer until tomatoes have slightly broken down, 3 to 5 minutes. Add shrimp; cook until opaque, 3 to 4 minutes. Remove from heat.
Add sour cream and lime juice to skillet; stir to combine. Serve hot.
Jalapenos get their heat from the seeds and ribs. If you don't like your food too hot, scoop out the thick white pith before chopping the flesh. For a hotter dish, chop the entire chile.