Preheat oven to 200°C / 390°F.
Prepare the sea bass. Clean and prepare the sea bass. Rinse well and then pat dry. using a sharp knife, make an incision lengthwise on both sides, right in the center of the body where the main bone is.
Drizzle with olive oil and season generously with sea salt. Place on a sheet pan lined with parchment paper.
Prepare the beetroots. Cut the tops and bottoms of the beetroots. Peel them and rub them with a paper towel to remove any remnant dirt. Slice them about 1 cm (almost ½-inch) thick.
Add the beetroot in a mixing bowl and drizzle with olive oil. Season with salt and toss to combine. Lay the beetroot slices next to the fish without stacking them.
Bake for about 20 minutes if the fish is 400 grams or 25 minutes if the fish is around 500 grams. To see if the fish is done check to see if there is any sign of blood right in the center where you made the incision. If not the fish is cooked.
In a mixing bowl combine garlic, 2 tablespoons olive oil, and 2 tablespoons vinegar. Toss in the beetroot slices and stir well.
Prepare the fish dressing. In another bowl whisk together 3 tablespoons olive oil, 2 tablespoons lemon juice, and 1 teaspoon dill.
Serve. Transfer the fish to a serving plate. Drizzle with the fish dressing. Add some of the beetroots on the side or just leave them in the bowl and serve as a side salad. Enjoy!