Peel the shrimp leaving tails intact. Slit open on the back and remove the vein. In a food processor, grind the garlic, ginger, spring onions and chilies to a paste with oil. Transfer to a medium sized pan and cook for 2 minutes. Add the spices and coconut milk and cook for 4 minutes. Add ½ cup of water to the garlic and spice mixture and cook over medium heat for about 4 minutes. Add the shrimp and cook until tender. Stir in the fresh coriander and serve over rice.