Red wine vinegar barramundi ceviche with beetroot salad

A delicious summer entree, with a barramundi ceviche of my own invention, and fresh young summer vegetables.
The ceviche is made ahead of time--at least 6 hours, or even overnight.
For up to 4 people, you need: one medium-size fillet barramundi, half a cup red wine vinegar, salt, pepper, herbs, half a chopped red onion, chopped garlic chives, one small young beetroot, and sliced fresh tomatoes. As well, a seasoning for the beetroot made of extra virgin olive oil, vinegar of your choice(I used white balsamic, but others can be used), and Dijon mustard.
First, hours before you are going to eat it, you cut the barramundi into pieces. Lay it in a container, grind sea salt and pepper over it then add the red wine vinegar. It should cover the pieces of fish. Cover and put in fridge for several hours or overnight.
To serve, first prepare the beetroot salad by peeling then grating the beetroot. Mix it with some chopped garlic chives, and the oil and vinegar and mustard dressing. Chop the red onion into small pieces, slice the tomatoes. Lay the beetroot salad on an entree plate, arrange pieces of the fish on top , then top with chopped onion and chopped garlic chives. Arrange the sliced tomatoes around it.
Enjoy!