Red onion, lemon, and tarragon come together as a tangy topping for salmon and asparagus. To make this recipe for two, as seen on "The Martha Stewart Show," halve the ingredient quantities.
Preheat oven to 400 degrees. Cut out four 12-by-17-inch pieces of parchment; fold each in half crosswise to form a crease, then open.
Divide asparagus and radishes evenly among 4 parchment pieces, arranging mixture on 1 side of each crease. Lay 1 salmon fillet on top of each pile. Season each with 1/8 teaspoon salt and some pepper.
Toss together onion, zest and juice, tarragon, 2 teaspoons oil, and 1/2 teaspoon salt; divide among salmon, spooning over tops. Fold parchment over ingredients; make overlapping pleats to seal.
Bake on 2 baking sheets (2 packets per sheet) for 11 to 12 minutes for medium-rare or 13 minutes for medium. Unwrap; drizzle fillets with remaining 2 teaspoons oil.