Preheat the oven to 350 degrees F. Place the beets on a jelly roll pan, toss with the oil, and cover tightly with aluminum foil. Bake until the beets are tender when pierced with a sharp knife, about 2 hours. Refrigerate until chilled. Peel the beets and slice into 1/16th-inch rounds. On 6 dinner plates, arrange overlapping beet slices in a wide circle. Cover tightly with plastic wrap and refrigerate until ready to serve.
In a small bowl, mix the goat cheese, blanched tarragon, parsley, chives, and thyme. Cover with plastic wrap and refrigerate until ready to serve.
To serve, uncover the plates and season the beets with salt and pepper. In a large bowl, toss the mesclun greens with the walnut vinaigrette to taste. Place the greens in the center each plate. Top with equal portions of the goat cheese. Garnish with the julienned beet and walnut halves. Drizzle and few spoonfuls of walnut vinaigrette around the inside of each plate, and serve immediately