Preheat the oven to 400°F or heat a grill to medium-high.
Spread the beetroot slices on a baking sheet or grill pan. Drizzle with olive oil and toss to coat. Roast or grill for 20 to 25 minutes, turning once, until tender and lightly caramelized.
Add the greens to a large bowl. Top with the warm beetroot, goat cheese, and walnuts.
Drizzle with vinaigrette and toss gently until everything is lightly coated. Season with salt and pepper to taste.
Serve right away while the beetroot is still slightly warm.