Slice the plantain and fry at 300°F until golden brown. Remove from oil, let cool, then sprinkle with salt and set aside. These will serve as the chips for the ceviche.
In a mixing bowl, combine 3 cups mahi-mahi and ⅓ cup lemon juice. Let the fish cure for 10 minutes.
In a pan over low heat, lightly sauté ½ cup sweet potatoes and ½ cup corn with 2 tablespoons olive oil, ½ tablespoon salt, and 1 teaspoon black pepper for about 7 minutes until tender. Remove from heat and let cool completely.
Mix together the cured fish, sautéed sweet potato and corn, ⅓ cup red bell pepper, ⅓ cup red onion, and ⅓ cup cilantro. Taste and finish with additional salt and pepper as needed.
Plate the ceviche and garnish with the plantain chips on top. Serve immediately alongside a glass of Domaine Carneros Ultra Brut.