Peel the plantains by cutting off the ends and making a lengthwise slit in the skin. Carefully remove the skin and slice the plantains into 1-inch thick pieces.
In a large skillet, heat about 1 inch of vegetable oil over medium heat. Once hot, add the plantain slices in batches and fry for about 3-4 minutes on each side until golden and slightly soft. Remove from the oil and drain on paper towels.
Using the bottom of a glass or a flat surface, gently smash each fried plantain slice to about ½ inch thick.
Return the smashed plantains to the hot oil and fry again for 2-3 minutes on each side until they are crispy and golden brown. Drain on paper towels and season with salt.
In a bowl, mix the black beans with cumin, garlic powder, onion powder, salt, and pepper. Mash slightly with a fork to combine.
Top each crispy tostone with a spoonful of the black bean mixture and garnish with chopped cilantro.
Serve warm with lime wedges on the side for squeezing over the tostones.