Make the dressing: Place the shallots, vinegar, juice, and salt in a small bowl. Let stand 15 minutes. Whisk in 1/3 cup of the olive oil. Taste. Adjust with more olive oil to taste — there should be nice balance of sweet and sharp in the dressing, and it will be on the thin side.
In a large bowl, combine the cabbage, fennel, scallions, greens, candied pepitas, shaved Manchego, and pepper. Pour over some of the dressing. Toss. Taste. Adjust with more dressing or salt or pepper to taste.