Heat the olive oil in a large skillet over medium-high heat. Season the mahi-mahi with salt and pepper. Cook the fillets in the hot oil until the fish is golden brown on each side, and no longer translucent in the center, about 3 minutes per side.
Meanwhile, whisk together the sour cream, lime juice, ginger, cumin, cayenne pepper, salt and pepper to taste; set aside. Gently combine the mango, pineapple, avocado, and jalapeno in a bowl.
To assemble, place a cooked mahi-mahi fillet into the center of a warmed tortilla. Place a scoop of the mango salsa onto the fish, then drizzle with the sour cream sauce, and finish with a generous pinch of chopped cilantro.