Today I used 50/50 mackerel and snapper, but I suggest going to a market and seeing what they suggest for ceviche from what they have on that day.
Broil or grill the corn with some butter and salt to brown. Let cool. Dice up the tomatoes and put in a large bowl. Chop the corn off the cobs and add to the bowl. Dice the pepperoncini and add along with the juice. Rip up the basil into smaller pieces and add to bowl. Mix and season well.
Meanwhile, juice all the lemons and oranges. Cop the fish into cubes roughly the same size as the tomato chunks. Pour the citrus over the fish chunks and season well. Grate the garlic into the bowl and add the chile flakes. Mix well. Dice up the red onion and top the ceviche mixture with the onion, pressing it down into the fish to keep the fish nicely submerged. Place this mixture into the fridge and allow the fish to cure for about 45 minutes, stirring once halfway through.
Finally, dump the fish mixture into the tomato mixture and mix well. Cut a baguette into crostini rounds and toast. Serve the ceviche with the bread.