1 medium onion, halved and thinly sliced
1 clove garlic, minced
1 hot Indian pepper
1 tsp each of cumin, coriander, turmeric
2 cups whole skinned tomatoes
¾ tsp. salt
¼ tsp. ground ginger
2 tablespoons oil
1 lb. cleaned and deveined shrimp
½ cup fresh cilantro
Cook onion in oil in a 12-inch heavy skillet over moderate heat, stirring occasionally, until golden, 6 to 8 minutes. Add pepper, garlic, and ginger and cook, stirring, until pepper is softened and garlic is golden, about 1 minute. Add cumin, coriander, salt, and turmeric (if using) and cook, stirring, until fragrant, about 1 minute. Add tomatoes and cook, stirring occasionally, until tomatoes break down and sauce is thickened, 3 to 5 minutes.
Add shrimp and cook, turning occasionally, until just cooked through, about 3 minutes. Remove skillet from heat and stir in half of cilantro. Serve sprinkled with remaining cilantro.