Bring the fish stock to a boil in a deep pot.
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In a skillet, sizzle the oil with chopped onions, minced garlic, sliced chillies, and paprika.
Then, add halved tomatoes and diced mushrooms and stir-fry the vegetables for 10 minutes.
Now, add the vegetables to the pot of boiling stock and simmer for a further 10 minutes.
Meanwhile, whisk the egg whites with potato starch in a bowl. Then, add the crab meat, making sure it's thoroughly drained, and the shrimp paste, and mix all into a thick paste.
Shape the crab paste into bite-sized balls, add them to the tomato broth, and cook for 10 minutes.
Meanwhile, cook the noodles in boiling water for 3 minutes, then drain them under cold water, and divide among serving bowls.
Pour a few ladles of tomato broth in each bowl and top with the crab balls. Serve with a side bowl of mint leaves, shredded pak choi, lime wedges, and beansprouts.