Toss cabbage, apple, and green onions together in a large bowl.
Whisk vinegar, sugar, olive oil, vegetable oil, Dijon mustard, and red pepper flakes together in a saucepan over medium heat. Bring dressing to a simmer.
Pour hot dressing over cabbage mixture and toss to coat. Cover the bowl with plastic wrap and refrigerate until flavors blend and slaw is cold, at least 1 hour.