Wrap the beets individually in aluminum foil and place them on a sheet pan. Roast them for 50 minutes to 1 hour, depending on their size, until a small sharp knife inserted in the middle indicates that they are tender. Unwrap each beet and set aside for 10 minutes, until cool enough to handle. Peel the beets with a small, sharp knife over a piece of parchment paper to prevent staining your cutting board.
Meanwhile, whisk together the vinegar, olive oil, mustard, 2 teaspoons salt, and 1 teaspoon pepper and set aside. While the beets are still warm, cut each one in half and then each half into 4 to 6 wedges and place them in a large mixing bowl. As you're cutting the beets, toss them with half of the vinaigrette (warm beets absorb more vinaigrette), 1 teaspoon salt, and 1/4 teaspoon pepper. Taste for seasonings.
Place the arugula in a separate bowl and toss it with enough vinaigrette to moisten. Put the arugula on a serving platter and then arrange the beets, almonds, and goat cheese on top. Drizzle with additional vinaigrette, if desired, sprinkle with salt and pepper, and serve warm or at room temperature.