To smoke the salmon heat the woodchips in the smoker over a medium heat until the smoke turns gray. Salt the salmon and add it to the smoker, cover the smoker, turn down the heat to medium and cook the salmon for twelve minutes, turn the salmon over and cook on the other side until the fish is opaque (approximately 10 minutes) and cooked but still moist.
While the salmon is cooking, bring the chestnuts to a boil in salted water to cover, simmer for 7 to 10 minutes until tender when pierced with a knife. Drain and reserve the chestnuts. In a medium saute pan over high heat cook the shiitake mushrooms in the butter and soy sauce. When the mushrooms are soft add the washed spinach leaves, cover the pot and let the leaves wilt for one minute. Remove the cover. The spinach should be bright green and wilted fold in the chestnuts and taste for seasoning.
Remove the salmon from the smoker when it is cooked and serve it on the spinach.