For the sea bass
- Preheat the oven to 200ο C (390ο F) set to fan and put a rack inside to get very hot.
- Cut the lemon into slices and set it aside.
- Sprinkle the cavity of each sea bass with salt, pepper, add the lemon slices and the oregano.
- Spread the olive oil on the outside of the sea bass and sprinkle the coarse salt on both sides.
- Pour the water in a baking pan. Remove the hot rack from the oven and place it on the baking pan. Place the sea bass onto the rack and roast for 15-20 minutes.
- Remove from the oven and, with a piece of paper, discard the coarse salt from the outside of the fish.
- Set the water of the baking pan aside, into a bowl.
For the salad
- Cut the potatoes into irregular pieces and add them into a bowl.
- Add the vinegar, salt, pepper, and mix.
- Add the olive oil, the capers, the green part of the spring onion and the parsley finely chopped, the pepper cut into small cubes, and mix.
For the olive oil-lemon dressing
- In the bowl with the water of the baking pan, add the lemon juice along with the mustard, and whisk well with a hand whisk.
- Add the olive oil very slowly by whisking constantly until the dressing is thick.
- Serve the sea bass with the olive oil-lemon dressing, the salad, parsley, and pepper.