Heat vegetable oil in a saucepan over medium heat, add sliced onion, garlic, stir until translucent, then add petite bell pepper.
Add chopped tomatoes, stir and let simmer for 3 minutes, then add fish powder, locust beans powder, stir and let it simmer for 3 minutes.
Add cooked beans, salt, stir and let simmer for 5 minutes, then take off heat.
Peel and cut ripe plantain into thin slices.
Lay the plantain slices at the bottom of a dish, spread the beans stew on top evenly and continue the process with the remaining plantain and stew.
Cover with aluminium foil and bake in a pre-heated oven at 200c for 15 minutes.
Baked beans ready to serve.