To toast walnuts, preheat oven to 350 degrees F. Spread nuts in a single layer in a shallow baking pan. Bake in preheated oven for 5 to 10 minutes or until light golden brown, watching carefully and stirring once or twice so nuts do not burn.
Meanwhile, place rice vinegar, walnut oil, garlic, mint, salt, and pepper in a blender container or food processor bowl. Cover and blend or process until nearly smooth.
Combine the spinach and toasted walnuts in a large bowl. Drizzle spinach mixture with dressing; toss gently to coat. Place spinach in 10 serving bowls or plates. Arrange orange and/or grapefruit slices and figs on greens. If desired, add goat cheese.