Pour coconut milk into a large, wide frying pan and set over medium heat. Stir in curry paste. Finely chop onion and stir into sauce. Slice tomatoes in half. Squeeze out and discard seeds. Coarsely chop. Then stir into gently boiling sauce. Stir often, uncovered until sauce thickens, 7-10 minute Meanwhile, defrost shrimp according to package directions. Pat dry with paper towels.
Once sauce is almost as thick as you like, stir in shrimp and celery. Stir until shrimp are bright pink, 3-5 minute Remove from heat. Stir in green onions, coriander and lime juice. Taste and stir in salt or more lime juice if needed. Excellent served over jasmine rice.