1. Grate 1 teaspoon zest from 1 orange and reserve.
2. Remove peel and pith from oranges. Cut segments into a bowl.
3. Squeeze 1 tablespoon juice from navel oranges into a large bowl and whisk together with reserved zest, vinegar, oil, mustard, salt, and pepper.
4. Toss escarole, endive, and orange segments with dressing to serve.