Heat a large heavy bottomed stockpot over medium heat and coat the pot with cooking spray.
Cook the onion until translucent, about 5 minutes. Add the cayenne, garlic, curry powder, and ginger and cook for an additional 2 minutes, stirring constantly.
Add the tomatoes, coconut milk, and water and bring to a boil. Reduce to a simmer for 10 minutes.
Add the shrimp. Bring to a boil again and cook for an additional 1 minute. Season with salt and pepper. Serve.