Preheat your oven to 425℉ and line a large rimmed baking sheet with parchment paper.
Whisk together the oil, lemon juice, garlic, dill, salt, and pepper in a small bowl. Reserve 2 tablespoons of this marinade for the vegetables.
Pour half of the remaining marinade over the salmon fillets in a shallow dish. Let them marinate in the fridge while you prep the sweet potatoes and other ingredients.
Peel and thinly slice the sweet potatoes into ⅛-inch rounds. Toss them with half of the marinade and spread into an even layer on the baking sheet. Roast for 10 minutes.
After 10 minutes, remove the pan and shift the sweet potatoes to one side. Add the green beans and sliced onion, tossing them with the reserved 2 tablespoons of marinade.
Return the veggies to the oven and roast for an additional 5 minutes.
Create a space in the center of the pan for the marinated salmon. Add a slice or two of lemon on top of each fillet, sprinkle lightly with salt and pepper, and bake for 10-15 minutes until the salmon flakes easily with a fork.
Serve immediately with extra lemon slices, if desired, and enjoy!