Preheat oven to 425 degrees.
Wash broccoli and cut into 2-inch stalks. Peel and thinly slice garlic. Wash lemon and zest by removing just the yellow peel using the small holes on a grater. Chop pistachios.
Coat a large, rimmed baking sheet with cooking spray. Combine broccoli, garlic, 2 tablespoon oil, 1/2 teaspoon salt and 1/4 teaspoon pepper on the prepared sheet. Roast for 5 minutes.
Combine pistachios, chives, lemon zest, remaining 1 tablespoon oil, 1/4 teaspoon salt and 1/4 teaspoon pepper in a small bowl. Spread 1 teaspoon mayonnaise over each salmon portion and top with the pistachio mixture.
Move roasted broccoli to one side of the baking sheet and place the salmon on the empty side. Roast until salmon is no longer bright pink in the center and broccoli is just tender, about 8-15 depending on thickness.