Preheat oven to 425°F. Toss potatoes with 2 teaspoons oil in large bowl. Season with salt and pepper. Arrange potatoes in single layer on nonstick baking sheet.
Bake until crisp and golden, turning occasionally, about 25 minutes.
Heat 1 tablespoon oil in large nonstick skillet over high heat.
Add mushrooms; sauté until golden, about 4 minutes.
Add parsley and garlic; stir 1 minute.
Transfer to plate.
Add vinegar and stock to skillet; boil until reduced by half, about 1 minute. Cool slightly.
Whisk in remaining 1 tablespoon oil.
Toss greens and chives in large bowl with 2 tablespoons warm vinaigrette. Divide greens among plates. Arrange potato slices in circle atop greens on each plate. Mound mushrooms in center.