Place the fish cubes in a large bowl.
Pour the lime juice and lemon juice over the fish, making sure it’s completely covered. The acidity of the citrus juices will "cook" the fish.
Cover the bowl and refrigerate for about 15-20 minutes, or until the fish is opaque and firm.
In a separate bowl, combine the finely chopped red onion, serrano chilies (or jalapeños), diced tomatoes, and chopped fresh cilantro.
Season the mixture with ground cumin, salt, and black pepper. Mix well.
Drain the fish from the marinade, discarding the excess juice.
Gently fold the vegetable mixture into the marinated fish.
Adjust seasoning with salt and pepper if needed.
Garnish with diced avocado, cooked sweet potato slices, and corn rounds.
Enjoy your meal!