Put the water in a large-sized stockpot with a steamer basket attachment over high heat.
Scrub 6 beets and remove any obvious blemishes while leaving most of the skins on. Slice the beets into 1/4”-thick moons and half-moons.
When the water comes to boil, add the beets. Steam for about 15 minutes, or until the beets are fork tender.
Meanwhile, stir together 2 Tbsp lemon juice, 1½ Tbsp apple cider vinegar, 2 Tbsp fresh cilantro, and 3 Tbsp olive oil in a small bowl. Set aside.
Place a skillet over medium-low heat and add ½ cup raw walnuts or pumpkin seeds. Toast them until they are fragrant and just barely turning a golden brown, about 5 minutes. Remove from heat.
Return the steamed beets to a large mixing bowl. Toss with the dressing.
Shred 1 fennel bulb and toss with 3 packed cups of lettuce or arugula. Pour the warm beets over the fennel/lettuce mixture and toss. Add the toasted walnuts or pumpkin seeds, ½ cup feta cheese (optional) and ground black pepper to taste