Bring water to a boil in a large pot.
Add pork stomach and boil for 10 minutes.
Discard the water to remove impurities.
Refill the pot with fresh water.
Add pork stomach, bananas, plantains, and yam.
Add onion, garlic, bay leaves, and oregano.
Season with salt, pepper, and annatto oil.
Bring to a simmer and cover the pot.
Cook for 1.5 to 2 hours until tender.
Check seasoning and adjust as needed before serving.