Heat oil in a cast iron skillet. Add sliced leek and onion. Cook until leek is translucent (3-5 minutes) then add garlic, clams, zest and juice from a half lemon. Cover and cook until some clams start to open (5-7 minutes).

Transfer the open clams to a bowl. Cover skillet and cook until remaining clams open. Discard any clams that don't open.

Remove all open clams from skillet. Add in beans, cilantro, scallion and season with salt and pepper. Loosen sauce with water, if it looks too thick.

Return clams to skillet and toss. Garnish with more fresh cilantro, lemon juice and drizzle with olive oil.