1. Preheat oven to 425°F (218C). Line a rimmed baking sheet with aluminum foil.
2. In a medium bowl, toss the squash with 1 tablespoon olive oil, a pinch salt and 1⁄4 teaspoon black pepper.
3. Spread on the prepared baking sheet and roast, stirring once for 15 minutes.
4. Remove the pan from the oven and move the squash to one side. Place the salmon fillets on the foil and sprinkle each with salt and pepper.
5. Return to the oven and bake 5 to 10 minutes, turning halfway through cooking time. The salmon is finished when it flakes easily with a fork.
6. Meanwhile, in a small bowl, whisk together the lemon juice, olive oil, garlic, tarragon and Dijon mustard.
7. In a large bowl, add the spinach and half of the vinaigrette and toss to combine.
8. Divide the spinach between four serving plates, top with 1⁄4 of the butternut squash and a salmon fillet and drizzle with some of the vinaigrette.

‍