Place oil in a medium-sized bowl and microwave for approximately 1-2 minutes. Stir in PBfit and mix until smooth and creamy. Add powdered sugar one cup at a time. Add water if needed. Stir until smooth.
Spread into an oiled 8 by 8-inch pan lined with parchment paper. Chill for at least 2 hours. Cut into 1-inch cubes. Store in an airtight container in the refrigerator. Enjoy your 4 ingredient Peanut Butter Fudge!