Heat oil in a nonstick skillet over medium-high heat. Add onion to pan; sauté 1 minute. Add sage, salt, and mushrooms; sauté 11 minutes or until mushrooms are browned. Add wine; cook 30 seconds or until liquid almost evaporates. Stir in Roasted Chicken Stock. Boil; cook until reduced to 2 cups (about 14 minutes).
Combine flour and water in a bowl, stirring until smooth. Add flour mixture to pan; return to a boil. Reduce heat; simmer 2 minutes or until slightly thickened, stirring occasionally. Remove from heat. Stir in butter, 1 tablespoon at a time, stirring until butter melts. Stir in pepper.
Add 1 tablespoon flour to the slurry for a thicker gravy. You can substitute fat-free, lower-sodium chicken broth for the Roasted Chicken Stock—but if you do, decrease the salt to 1/8 teaspoon or add none at all.