Add the fresh ginger (no need to peel it), star anise and chopped garlic and onion to a large casserole. Drizzle with the olive oil.
Place the casserole over medium heat. Gently fry the ingredients for 3 minutes. Then add the prawn heads and shells.
Stir and bake the heads for 2 minutes. Then add the water and fish bouillon.
Also add the tomato, chili powder (or chili paste) and tomato paste.
Bring the prawn soup to a boil. Then turn the heat lower and simmer for 20 minutes. Take the soup off the heat and let it cool down. Then blend or mix the prawn soup until the ingredients are turned into a fine pulp.
Pour the soup through a fine sieve (you can place a cheesecloth in it as well) over another large casserole and stir it until you end up with the shrimp pulp. Press well using the back of a spoon to get as many liquid out of it as possible.
Discard the pulp. Place the sifted soup back over medium heat. Check the seasoning and add extra chili powder or paste and fish bouillon to taste. Once the soup is warm, add the soba noodles and cook them for 3 minutes until tender.
Then scoop the noodles and prawn head soup into large bowls. Serve hot.