How to Make It
Heat 1 1/2 teaspoons oil in a large skillet over medium-high. Sprinkle fillets evenly with 1/2 teaspoon salt and 1/4 teaspoon pepper. Add fillets to pan; cook 4 to 5 minutes on each side or until desired degree of doneness. Cool 5 minutes. Break fillets into large flakes with a fork.
Combine remaining 2 1/2 tablespoons oil, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, tarragon, vinegar, and garlic in a large bowl, stirring with a whisk. Add fennel, mint, parsley, and spinach; toss to coat. Arrange spinach mixture on plates; top with salmon.