For the beans: Place the oil in a sauce pan. Add the onions, garlic, red bell pepper and cook for about 5 minutes.
Add the cooked beans, salt, pepper and cumin. Stir and cook for about 5 minutes more. Set aside.
For the plantains: In a medium skillet, melt the butter and add the diced plantains. Brown the plantains for about 3 minutes and set aside.
To assemble the arepa: Place an arepa on a serving plate, top with the beans, sprinkle the cheese and add the plantain and guacamole on top.