In a medium bowl, dissolve the orange-flavored gelatin in boiling water, stirring continuously for 2 minutes until completely dissolved.
Add the cold water to the dissolved gelatin and mix well.
Refrigerate the gelatin mixture for approximately 1 hour or until partially set (consistency should be similar to unbeaten egg whites).
In a separate large bowl, gently combine the cottage cheese, drained mandarin orange segments, whipped topping, and marshmallows if using.
Once the gelatin has reached the partially set stage, remove it from the refrigerator and fold it gently into the cottage cheese mixture until evenly combined.
If using any optional ingredients like nuts, coconut, or orange zest, fold them in now with a few gentle strokes.
Transfer the completed orange jello salad to a decorative serving dish or individual serving cups.
Cover and refrigerate for at least 2 hours or until completely set.
Before serving, garnish with additional mandarin slices, a dollop of whipped topping, or fresh mint leaves if desired.