Soak cedar plank boards for at least 2 hours. (I’ve read that you can soak and freeze boards to use later, but have not tried this method.)
Preheat oven to 375F.
Lay salmon on first board. Cut lemon in half. Mix 1T lemon juice with honey and mustard. Brush salmon with sauce and if desired, top with a lemon slice.
Wash and cut potatoes into wedges.
Mix potatoes with oil and seasonings. Spread them out evenly on the second board.
Lay broccoli on the third board, spray liberally with a misto or cooking spray, sprinkle with lemon pepper.
Put boards on top of a cookie sheet and place in the oven. Bake for 5 minutes before turning down the oven to 350F for 30-40 minutes. Check meal frequently, likely the broccoli will be done at the same time as the salmon. My potatoes required an extra 15 minutes.
Some of the following steps were recommended on other sites, but I skipped them:
Some sites say to oil the boards prior to adding food.
Some sites recommended boards heat up with the oven.