Since the spinach in this dish is only lightly steamed, it is very important to make sure it is washed thoroughly. The leaves should still be wet for cooking.
Place the spinach in a large pot with a tight-fitting lid. Cover and cook over high heat, turning leaves halfway through to move the bottom wilted leaves to the top, until the spinach is just barely wilted and tender, about 4 minutes.
Lift the spinach into a warm serving dish. Drizzle over the olive oil and the juice from half the lemon. Sprinkle on the salt and pepper and toss to combine. Serve with the remaining half lemon for those who want to squeeze on a little extra.