Soak a packet of bihun in plain water.
Chop two red onions and three garlic cloves, then blend them.
Add chopped chili if you like it spicy; adjust to taste.
Add seafood: fish cakes and balls (optional).
Blend shrimp paste if using (optional), add a half cup of oyster sauce, four tablespoons each of sweet soy sauce and tomato sauce, and two tablespoons of chili sauce.
Blend the ingredients until well mixed.
Kacau the bihun with the mixture; it may not seem to absorb the sauce initially but will become tender as it cooks.
Add fish sauce and salt to taste. Continue cooking until the bihun is soft.
Slice a large onion thinly and add to the bihun along with sliced garlic, and mix well.
Serve with condiments like fried bread or crackers, and garnish with chili peppers if desired.