Add the onion, bell pepper, njansa, country onion spice, African nutmeg, and a 1/4 cup of water in a blender. Purée.
Add the purée to the plantain flour, palm oil, warm water, and chicken bouillon. The consistency should be similar to pancake batter.
Rinse the whole catfish under warm water quickly to wash away any slime.
Cut into 4 steaks and add to the plantain batter.
Place a catfish steak in the center of the banana leaf with a scoop or two of the plantain batter.
Wrap and tie up, making sure that none of the batter pours out.
Do the same to the other catfish steaks.
Place the banana leaf packages in a steamer pot. Steam over high heat for an hour, making sure that there is always enough water in the pot. Let rest for 20 minutes before serving.