Heat 3 tbs of the butter and 2 tbs of the oil in a large frying pan until butter has melted. Add half 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 1 tbs butter and 2 tbs 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.