Preheat the oven to 400°F (200°C).
Wrap the unpeeled beets in foil and place them on a baking sheet.
Roast the beets for 40 to 45 minutes until fork-tender.
Allow the beets to cool for 10 minutes, then peel the skins by rubbing with a paper towel.
Slice the peeled beets into cubes or rounds.
Segment the oranges, removing all white membranes.
Slice the avocados just before assembling the salad to prevent browning.
If using greens, layer them on a serving platter or bowl.
Top the greens with the roasted beets, orange segments, and avocado slices.
Whisk together olive oil, fresh orange juice, vinegar, Dijon mustard, maple syrup or honey, salt, and pepper to create the vinaigrette.
Drizzle the vinaigrette over the assembled salad.
Sprinkle toasted pistachios or walnuts, optional cheese, and fresh herbs on top.
Serve the salad immediately for best freshness.