Bring a couple inches of water to boil in a large pan, or pot. Sit a steamer basket on top, careful to not make contact with the water. Lay the potato slices in the steamer basket in one layer. Sprinkle with salt & pepper. Lay the salmon filet over the potatoes, & sprinkle with salt & pepper. Cover & steam for 8 minutes. Place the green beans in the steamer basket, on top of the salmon. Squeeze one half of the lemon on top of the steamer contents. Cover & steam for an additional 6-8 minutes.