1. Preheat oven to 400°.
2. Arrange salmon in a single layer on a jelly-roll pan coated with cooking spray. Combine sesame seeds and 3/8 teaspoon salt; sprinkle evenly over flesh sides of fillets, pressing gently into fish. Bake at 400° for 14 minutes or until desired degree of doneness.
3. Melt butter in a medium saucepan over medium heat. Add oil to pan; swirl. Add green onions; cook 2 minutes, stirring occasionally. Add lemon slices; cook 2 minutes. Sprinkle green onion mixture with remaining 1/8 teaspoon salt and pepper. Place 1 fillet on each of 4 plates. Place arugula in a medium bowl. Add green onion mixture to bowl with arugula; toss. Divide arugula mixture evenly among servings.