Cut the avocados into little pieces. Mix them with the lemon juice and a few sprigs of finely chopped coriander until you obtain a cream. Leave in a cool place.
Cut the fish in little pieces and place in a bowl. Leave in a cool place.
Divide the mango into little cubes, cut the green onions into large pieces and coarsely chop a sprig of coriander.
Mix the fish, mango, pieces of green onion, olive oil, juice of the second lemon and white balsamic vinegar with lemon and the coriander.
Add salt and pepper to taste. Put in a cool place for 30 minutes. Your ceviche is ready.
Serve the cream of avocado as a side dish.