Dissolve jello and marshmellows in pineapple juice; once done pour into bowl and place in refrigerator to allow the jello to begin setting. (you want it to be firm, but not completely set as normal jello would be if you made it with water; approximately 1/2 the consistancy of normal jello).
Once the jello has set to 1/2 the consistency of normal jello, mix the remaining ingredients into bowl - pineapple, cottage cheese, walnuts and cool whip. Place back into refrigerator and allow to completely set.
This is a great dish for picnics, pot lucks, holiday dinners, birthdays or even if you want to make a treat for the kids. My brother insists that we make it every year.