In a large pot, combine the pork belly, chicken, fish, shrimp, onions, garlic, bell peppers, thyme leaves, cilantro leaves, bay leaves, black pepper, salt, and water.
Bring the mixture to a boil over high heat.
Reduce the heat to medium-low and let simmer for 30 minutes.
Add the green and ripe plantains, cassava, and yams to the pot.
Cover the pot and let simmer for another 30 minutes or until the vegetables are tender and the meats are cooked through.
Remove the pot from the heat and let cool for a few minutes.
Serve the Belizean Boil Up hot in bowls.