Preheat oven to 400 and line baking sheet with parchment paper.
Add the asparagus and radishes to the baking sheet. Drizzle with 2 tbsp olive oil, 1 teaspoon salt and 1/2 teaspoon pepper. Toss to coat evenly.
Scoot the vegetables over on either side to create a large enough space for the salmon. Place the salmon in the middle of the sheet pan. Drizzle the salmon with 1 tablespoon olive oil and brush to coat evenly, then season with 1/2 teaspon salt and 1/4 teaspoon black pepper.
Place sheet pan in oven and roast for 12-15 minutes, until salmon is cooked through and vegetables are tender.
For the Lemon Tarragon Sauce:
In a food processor or blender, add the lemon juice, mayo, garlic, tarragon leaves, salt and pepper. Blend until well combined.