Boil the plantains in enough water to cover it, adding the salt to the water, until the plantains are very tender (about 15 mins). Remove from the water.
Mash the plantains with a fork until it is a small puree with no lumps. Mix in the water. Set aside for a moment.
Heat 3 tablespoons of oil over very low heat, stir in the onion. Cook stir until the onion starts to become translucent. Remove from the heat and mix with the mashed plantain. Allow it to cool to room temperature.
Heat oven at maximum temperature. Grease a mini-muffin mold with the rest of the oil.
Once the plantain has cooled down, scoop two tablespoons of the mixture at a time and make into balls.
Place the balls into mini-muffin molds and press to form the cups. Place a cheese cube into each cup.
Whisk the egg and mix in tomato, chives, salt and pepper. Pour this mixture into each cup enough to fill them.
Bake until the eggs have set. Remove from the oven, and let it rest for a couple of minutes. Use a skewer to help you unmold them and serve warm.