Divide the greens between two bowls or plates and arrange into a ring.
Using a sharp knife, cut the salmon into small, 1-inch chunks onto a cutting board, and then chop the fish into a fine dice, letting the salmon spread out on the cutting board into a rough rectangle.
Zest the lemon over the salmon, and then add the scallion, capers, kosher salt and black pepper and mix it gently with your hands to combine. Divide the salmon mixture between the two bowls.
Cut the zested lemon into wedges and use one wedge per bowl to squeeze lemon juice onto the greens (avoid the salmon at first), and then drizzle the olive oil over both bowls. Garnish with a little flaky sea salt, if desired, and serve with the remaining lemon wedges to squeeze onto the tartare to your taste.
