Preheat the oven to 200°C.
Boil the whole potatoes in their skins for seven minutes then drain.
Peel and coarsely grate the potatoes once cooled.
Mix the potato with onion and garlic and season.
Form the mixture into four flattened patties and refrigerate for 20 minutes.
Heat oil in a pan and fry the rosti for 5 minutes per side until golden.
Drain the cooked rosti on kitchen paper.
Fry bacon lardons in a clean pan until golden-brown.
Stir in the chilli, tomatoes, and coriander then transfer to a bowl.
Mix in cubed avocado and olive oil and season to taste.
Season sea bass fillets with salt and pepper.
Heat olive oil in an ovenproof pan and fry fillets skin-side down for two minutes.
Flip the fillets and roast in the oven for 3 minutes.
Serve the fish on top of the rosti with a spoonful of salsa.