Peel and de-vein the shrimp leaving on the tails, and set aside. Cut the vanilla beans into 1-inch pieces with a knife, and then chop to a fine bread crumb texture in a small food processor or spice grinder, about 1 tablespoon. Set aside.
Cut off the brown ends of the plantains and slit the skin lengthwise from end to end along its ridges, preferably with a table knife. With your fingertips, work off the skin. Slice crosswise into 1/4-inch rounds or at an angle. Heat the vegetable oil over moderate heat in a medium-sized, heavy bottomed saucepan or deep skillet until barely rippling (about 350 degrees F). Fry the plantain rounds until golden, for about 1 to 2 minutes. Remove from the skillet and place on paper towels to drain. Keep in a warm place.
Place the tomatoes and chiles in a blender or food processor and process to a fine puree. Heat the olive oil in a 9-inch skillet or medium saucepan over medium heat until it ripples. Stir in the puree and salt. Saute stirring occasionally for approximately 20 minutes or until the sauce thickens and the oil starts to separate from the solids and begins to fry again.
Stir in the onions, the ground vanilla, the vanilla extract, the optional sugar, and the dark chocolate, and cook until the chocolate dissolves, about 3 minutes, while stirring. Add the shrimp and the plantains and cook for 3 more minutes. Serve immediately with white rice or Moors and Christians rice.
Serving Suggestions: White rice or Moors and Christians rice.