Spread the bread in a single layer on a sheet pan and mix with 1 tablespoon olive oil, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. The bread should be toasted for 15 to 17 minutes, stirring halfway through, until golden brown.
In a small bowl, combine the Dijon mustard, white wine vinegar, olive oil, kosher salt, and black pepper to make the vinaigrette.
In a sizable bowl, mix the brussels sprouts, apples, scallions, walnuts, blueberries, Manchego, and parsley. Drizzle the vinaigrette over the mixture.