Peel and devein the shrimp. Save the heads and shells for the stock.
Soak the noodles in lukewarm water until softened but still firm. Drain and set aside.
Cook the shrimp heads and shells in oil until lightly browned. Add water, salt, pepper, and a bay leaf. Bring to a boil, then simmer for about 5 minutes.
Add the shrimp to the boiling stock and cook until pink and opaque, about a minute. Strain the stock, then set the shrimp aside.
Boil the eggs for 10 minutes. Transfer to cold water, then peel and slice.
Cook the ground pork in a wok or large pan until browned. Season with salt, then push to one side.
Add the garlic and onion, then cook until softened.
Add the tinapa flakes and cook until lightly browned.
Stir in the annatto powder, then add the shrimp stock. Add more water if you like more sauce.Season with fish sauce and black pepper. Bring to a boil, then taste and adjust. Stir in the cornstarch slurry. Simmer until thickened.
Cook the soaked noodles in boiling water until tender but not too soft.
Drain the noodles, then arrange on a platter or divide into servings. Spoon the sauce over the top, then add the toppings. Serve with calamansi or lemon on the side.