Stir in tomato paste and tamarind concentrate, and fry for a few seconds to mix well with the spices and onions. Throw in chopped tomatoes, season with salt and cook covered till tomatoes start to soften and pulp.
Slowly add in the shrimp, and stir-fry with the tomato mixture to coat. Cook covered for a few minutes till shrimp is cooked through, garnish and serve warm.