Preheat the oven to 425ºF.
Arrange the diced sweet potatoes on a sheet pan. Drizzle with olive oil. Top the sweet potatoes with salt, pepper, and cumin, toss to combine. Bake the sweet potatoes for 15 minutes.
While the sweet potatoes are baking, prepare the salmon. In a small bowl, combine the butter, lemon juice, garlic powder, pepper flakes, thyme, salt and pepper. Heat in the microwave for 15 seconds or until the butter melts. Line a small baking sheet with foil, spray with cooking spray. Place the salmon fillets on top. Drizzle with the prepared lemon sauce.
When the timer on the potatoes goes off, remove and toss. Place back in the oven along with the broccolini and salmon for 12-15 minutes. Check on the salmon around the 8 minute mark. Salmon is done when firm to the touch. Baking time will vary depending on the thickness of the fillet.
Divide the veggies and salmon into containers and allow to cool slightly before refrigerating.