The day before making the ceviche, place sliced onions in a medium saucepan and cover with water; bring to a boil, remove from heat, then strain onions and set aside.
In the saucepan, combine vinegar, black pepper, cumin seeds, oregano, garlic, sugar, salt and beet; bring to a boil, reduce heat and simmer 7 minutes.
Add the onions and simmer an additional 7 minutes.
Place mixture in a covered container and refrigerate at least one day.
This makes more than is needed for the ceviche, but the pickled onions can kept up to a month, in the refrigerator, and used in other dishes, like salad, and as a garnish.
To make the ceviche, place fish in a large glass or other nonreactive bowl; cover with lime juice and allow to marinate for about 20 minutes, stirring occasionally.
Drain fish, but reserve 1/4 cup of the lime juice.
To the fish, add the onion, chile peppers, ginger, oil, cilantro and chile paste; stir in the reserved lime juice.
Chill thoroughly (I chill overnight).
Drain ceviche and season to taste with salt.
Serve in a chilled martini glass, if desired, and garnish with plantain chips or tortilla chips, pickled red onions, and slices of avocado.