Prepare the Beets
Preheat the oven to 400F. Prep beets by trimming off the long root end, stems, and greens (reserving stems and greens for another use). Wrap the beet tightly in foil and roast in the oven on a foil-lined sheet tray for one hour. Allow the beet to cool, peel off the skin, quarter and then thinly slice.
Make the Vinaigrette
In a small bowl combine lemon juice, dill, and olive oil until fully incorporated. Season with salt and pepper to taste.
Bring it all Together
Assemble the salad onto individual plates or a large platter by layering beets, mandarins, smoked salmon, and fennel, drizzling with vinaigrette as you go. Top with spoonfuls of avocado, crumbled feta, and more vinaigrette. Finish with freshly cracked black pepper and fennel fronds.