Heat oil in a large skillet over medium heat. Add chopped onion and salt. Cook, stirring occasionally, until onion begins to soften. Add 2 tablespoons of tomato paste, curry powder and fresh ginger. Cook, stirring to break up paste, until mixture is smooth and fragrant, about 1 minute.
Add 1 chopped tomato to skillet, cook, stirring, until it begins to release juices. Add 1/4 cup vegetable broth and simmer until tomatoes have slightly broken down, 3 to 5 minutes.
Add one can of coconut milk and the lime juice to skillet; stir to combine and let it simmer until the sauce thickens. Add shrimp, salt and pepper; cook until shrimp are opaque.
Serve hot over basmati rice, garnished with fresh herbs and a wedge of lime, if desired.