On a rimmed baking sheet, toss the beets, carrots, sweet potatoes, baby potatoes, and Brussels sprouts with the olive oil. Season with salt and black pepper. Roast for about 20 minutes, or until the veggies are slightly tender.
MEANWHILE, MAKE THE PESTO. In a food processor, combine the sage, kale, and pistachios and pulse until finely chopped. Add the Parmesan, if adding, and pulse again. With the motor running, drizzle in the olive oil. Season with salt and red pepper flakes.
Remove the veggies from the oven and push them to one side of the pan. Put the salmon on the other side. Rub a few tablespoons of the sage pesto over each fillet.
Return the pan to the oven and roast for 10 to 20 minutes more, until the salmon reaches your desired doneness and the veggies are soft.
If desired, squeeze a drop of lemon juice over the salmon. Serve with the roasted veggies and extra sage pesto alongside.