Heat ¾ of the butter and ¾ of the oil in a large frying pan until butter has melted. Add some of the plantain slices and cook for 2-3 minutes on each side, or until golden brown. Using tongs, transfer plantain slices to a large bowl, covering with foil to keep warm. Repeat with remaining slices.
For the spicy mojo, heat remaining butter and oil in same pan until butter has melted. Stir in garlic, remove pan from heat and stir in remaining ingredients until well blended.
Pour the spicy mojo over the plantains in a bowl and coarsely mash until well blended. Serve immediately.
If any plantain does not peel easy, cut off the end of the plantain. Using a sharp knife, carefully make 4 lengthwise slits just to the flesh of the plantain on opposite sides of the plantains skin. Peel off the sectioned pieces of the skin to expose the flesh of the plantain. Cut each plantain into 1cm slices.
If not using plantains immediately, soak them in salted water to prevent them from browning. Drain and pat dry.