1. Preheat oven to moderate (350° F.). Rub the game hens or squabs with the lemon half and sprinkle inside and out with salt and pepper.
2. In a skillet heat two tablespoons of the butter, add the chicken liver halves and cook until barely done. Remove from the pan and chop fine.
3. Heat the remaining butter in the same skillet, add the mushrooms and cook briefly. Combine the livers, mushrooms, ham and pistachio nuts and stuff the game hens or squabs lightly with the mixture. Close the opening with skewers and string and tie the legs with string.
4. Place the birds, breast side up, on a rack in an open roasting pan and cover the breasts with the bacon slices. Roast, basting occasionally with the pan drippings, until tender, forty-five minutes to one hour.