In a large skillet or saucepan, preheat the oil over medium heat. Add the cinnamon and chilli flakes. Stir constantly for 1 minute.
Add the onion and cook it for 4-5 minutes or until it's golden.
Add the garlic and spices. Stir constantly for 1 minute.
Add the tomatoes and stir to incorporate.
Add the water and lower the heat to have a slow simmer. Let it thicken. At this point, the tomato should have begun to disintegrate. If it wasn't very ripe it could need a bit longer. In that case, add more water.
Once thickened, add the shrimp and coconut milk and stir. Add salt and taste. Let the curry bowl for just 3 minutes to prevent the shrimp from overcooking.