Preheat oven to 400ºF. In a medium bowl, gently toss sweet potatoes and brussel sprouts and onions with 2 Tbsp. olive oil and season with salt and black pepper. Place on baking sheet and put in oven; cook for 20-25 minutes until potatoes are fork tender.
Season salmon with salt and black pepper. Heat 1 Tbsp. olive oil in a large sauté pan over medium-high heat. Add salmon to pan, flesh side down. Cook for 2 minutes. Turn salmon over, cook for an additional 2 minutes. Move salmon to side of skillet and 1 tsp olive oil and set lemon aside and add vegetables to the pan. Squeeze lemon on top. Cover and cook for an additional 2 minutes salmon has reached an internal temperature of 145ºF. Remove salmon from the pan; keep warm. Add desired amount of sauce to the pan and heat for 1-2 minutes. Top salmon with sauce and serve with vegetables and sweet potatoes.