Place the beans in a bowl, add enough water to cover them, and let them soak for 10 to 15 minutes, or until the skins have softened.
Rub the beans between your palms to remove the skins, or place in a food processor and pulse a couple of times until the skins fall off. Then rinse and use a sieve to remove the floating skins and hulls.
Preheat your oven to 350°F. Place a pan half-filled with water on the lower rack of your oven. This helps create steam and keeps the Moi Moi moist while baking.
Add the peeled beans, pepper, and onion to a blender. Pour in just enough stock (or water) to help the blades move freely. Blend until the mixture is very smooth.
Pour the blended mixture into a large mixing bowl. Add salt, the seasoning cube, mackerel, vegetable oil, and palm oil.
Mix thoroughly with a whisk or wooden spoon. Lightly grease your muffin pan, ramekins, or baking dish with oil to prevent sticking.
Pour the batter evenly into the pan, filling each section about ¾ full to leave room for expansion.
Gently place slices or halves of hard-boiled eggs on top of each portion of batter. You can press them slightly into the surface.
Cover with a foil paper and place the pan in the middle rack of the oven
Bake for 30 minutes, or until the top is firm and a knife inserted in the center comes out fairly clean.
Remove the Moi Moi from the oven and let it cool for 5–10 minutes to set very well before unmolding.
Serve warm with garri, rice, bread, or pap (akamu) or enjoy on its own!