Preheat the oven to 400°F (204°C). Line a sheet pan with aluminum foil to prevent sticking and ease cleanup.

Place the cleaned beets on the prepared sheet pan. Rub the beets thoroughly with the olive oil, ensuring they are evenly coated. Sprinkle them lightly with salt. Cover the beets with a second sheet of aluminum foil, sealing the edges securely.

Transfer the covered sheet pan to the oven and roast the beets for 1 to 2 hours, depending on their size and freshness. After the first hour, test for doneness by inserting the tines of a fork into the center of a beet. Continue checking every 15 minutes. The beets are fully cooked once the fork inserts easily without resistance. Remove from the oven and allow to cool slightly.

While the beets cool, place the balsamic vinegar and sugar into a small, shallow sauté pan. Heat over high heat until the mixture begins to simmer. Reduce the heat and continue cooking until the vinegar thickens into a syrup-like glaze. Remove from heat and set aside.

Once the beets are warm but cool enough to handle, peel off the outer skins and discard them. Cut the beets into quarters or into smaller bite-sized pieces, according to preference.

Place the cut beets into a serving bowl. Drizzle the prepared balsamic glaze over them. Add the orange zest and season with additional salt and freshly ground black pepper to taste. Toss gently to combine. Garnish with extra orange zest if desired before serving.