Prepare the salsa. Heat vegetable oil in a deep fryer or 2-quart saucepan to 375 degrees F. Place plantain cubes in deep fry basket. Lower basket into hot oil and fry for about 3 minutes until golden brown. Remove plantain cubes from oil and place on a paper towel-lined plate. Allow to cool.
In a medium bowl, combine the plantain cubes with the mango, green pepper, red onion, jalapeno, cilantro, half of the minced garlic, 1/4 teaspoon sea salt and lime juice. Set aside.
In another medium bowl, place softened butter. Sprinkle with remaining 1/4 teaspoon sea salt and black pepper. Add remaining minced garlic and shallot. Stir to blend well. Set aside.
Heat grill to medium-high heat. Add steak. Cook the steak, turning once, until steak is cooked medium rare. Remove from grill to carving board. Place 1/2 of the garlic butter mixture on the top of the steak, spreading to cover. Allow to rest while preparing potatoes.
Place half of the sliced potatoes in deep fry basket. Lower into hot oil. Cook potatoes until lightly browned, for 3 to 5 minutes. Place remaining garlic butter into a shallow bowl. Remove potatoes from oil and allow to drain. Add potatoes to butter in bowl. Toss to coat. Fry remaining potatoes. Drain and add to potatoes in bowl. Toss to coat.
Thinly slice the steak.
To serve, place 1/4 of the potatoes onto each of 4 serving plates. Top each with 1/4 of the steak slices followed by 1/4 of the salsa. Garnish with cilantro sprigs and lime wedges. Serve immediately.