Preheat the Oven: Preheat your oven to 400°F (200°C).

Prepare the Potatoes: Toss the diced potatoes with olive oil, garlic powder, thyme, salt, and pepper. Spread them in a single layer on a baking sheet and roast for 25-30 minutes, flipping halfway through, until golden and crispy.

Prepare the Salmon: While the potatoes are roasting, mix the melted butter, lemon juice, garlic powder, parsley, salt, and pepper in a small bowl. Place the salmon fillets on a separate baking sheet and brush them generously with the lemon butter mixture.

Roast the Salmon: After the potatoes have been roasting for 15 minutes, place the salmon fillets in the oven and bake for 12-15 minutes, or until the salmon is cooked through and flakes easily with a fork.

Prepare the Broccoli: While the salmon and potatoes are cooking, toss the broccoli florets with olive oil, salt, and pepper. In the last 10 minutes of roasting, add the broccoli to the same baking sheet as the potatoes, or place it on a separate sheet.

Serve: Once everything is cooked, serve the lemon butter salmon with the roasted potatoes and broccoli on the side.