Combine oats, 1 cup water, and 1/2 teaspoon kosher salt in a medium saucepan; bring to a boil. Reduce heat, and simmer for 7 minutes (do not stir) or until liquid almost evaporates. Remove from heat; fluff with a fork. Place oats in a medium bowl, and let stand for 10 minutes.
Combine walnuts, honey, and red pepper in a small nonstick skillet over medium heat; cook 4 minutes or until nuts are fragrant and honey is slightly caramelized, stirring occasionally.
Combine remaining 1/2 teaspoon salt, olive oil, vinegar, and black pepper in a small bowl, stirring with a whisk. Add dressing, apple, radicchio, and grapes to oats; toss well. Place 1 1/2 cups oat mixture on each of 4 plates, and top each serving with about 3 tablespoons walnut mixture and 2 tablespoons blue cheese.