Heat oven to 425° F. Toss the carrots and mushrooms with the oil, ½ teaspoon salt, and ½ teaspoon pepper on 2 rimmed baking sheets.
Roast the vegetables, tossing once, until tender, 15 to 20 minutes. Toss with the lemon juice, and thyme.
Meanwhile, cook the quinoa according to the package directions.
Divide the spinach among plates and top with the warm quinoa and vegetables. Sprinkle with the pistachios and drizzle with the oil.