Sprinkle shrimp with salt and turmeric. Toss well to coat; cover and set aside for 15 minutes.

Combine mustard, cumin, garlic, ginger, chiles and lemon juice in a blender and puree. Set aside.

Heat oil in a large heavy skillet over medium-high heat. Add onions and cook until soft, about 3 minutes.

Add pureed spice mixture. Cook, stirring, until fragrant, about 5 minutes.

Stir in tomato and cook until soft. Add shrimp, stir gently to coat them evenly.

Pour in the water and bring to a boil, stirring constantly. Reduce heat to medium, cover, and cook until shrimp are just opaque, about 5 minutes.

Mound rice into heated serving plates. Spoon curry over and serve. Note: Basmati rice has a distinctive nutty flavor. It is available at Indian, Middle Eastern, some specialty food stores and supermarkets.