1/2 medium green cabbage, cut into 2-inch pieces 5 Tbsp. olive oil, divided Kosher salt and freshly ground black pepper 8 slices bacon, cut into 2-inch pieces 1/3 loaf (about 8 ounces) dark or marbled rye bread, torn into large chunks 3 Tbsp. apple cider vinegar 1 Tbsp. Dijon mustard 1/2 large red onion, sliced 1 large red apple, chopped 3 oz. blue cheese, crumbled (about 3/4 cup)
Preheat oven to 475°F. Line a rimmed baking sheet with aluminum foil. Toss together cabbage and 2 tablespoons oil on prepared baking sheet. Season with salt and pepper. Bake until edges are golden brown, 20 to 23 minutes.
Meanwhile, cook bacon in a large skillet over medium heat, stirring occasionally, until golden brown, 10 to 12 minutes. Transfer to a paper towel-lined plate with a slotted spoon.
Pour off all but 2 tablespoons fat from the skillet. Add bread and toss to coat. Season with salt and pepper. Cook, stirring occasionally, until crisp, 5 to 6 minutes.
Whisk together vinegar, mustard, and remaining 3 tablespoons oil in a bowl. Season with salt and pepper.
Add onion, apple, cabbage, bacon, bread, and blue cheese, and toss to combine. Serve immediately.