Place the dried beans in a large bowl and cover with plenty of water; soak for 3 hours or overnight. If short on time, you may skip soaking and add 1/5 teaspoon baking soda to the cooking water (optional).
Drain and rinse the soaked beans in a colander.
Transfer the beans to a large pot or pressure cooker and add enough water to come about 1 inch (2.5 cm) above the beans.
Simmer the beans until tender but not falling apart, adding more water if needed to maintain a thick porridge consistency.
Add the chopped onion and chopped plantain to the pot, then continue to simmer until the plantain pieces are soft.
Stir in the ground crayfish, the stock cube, and the red palm oil; season with salt and pepper to taste.
Reduce the heat to low and cook for a further 10 minutes to let the flavors meld, stirring occasionally.
Serve the beans and plantain porridge hot.