Peel and cube sweet potatoes. Place sweet potatoes in a pot and fill with water, ensuring the sweet potatoes are fully covered. Bring to a boil on high heat.
Cook sweet potatoes for about 5 minutes or until a fork can easily pierce the potato pieces. The potatoes should be tender, yet still firm.
When potatoes are cooked, remove from heat and drain water completely. Transfer potatoes into a bowl and refrigerate for a few hours until chilled.
While the sweet potatoes are cooling in the refrigerator, make the dressing by combining the olive oil, palm shortening, lemon juice, and ½ tsp salt in a bowl.
Using an immersion blender or traditional blender, blend ingredients on high until liquid becomes creamy. This should only take about 1 minute.
Next, add the stoneground mustard. Mix until combined; then refrigerate.
Fry bacon until crispy. Remove from heat and allow bacon to cool. Roughly chop the bacon into small bite-sized pieces and set aside, refrigerating if prepared in advance.
After the sweet potatoes have chilled, take them out of the refrigerator.
Finely dice the red onion, celery and cucumber. Add these vegetables and the dressing to the potatoes. Stir to combine until the potatoes are evenly coated with the mixture.
Add salt and pepper to taste. Add the bacon and lightly stir to distribute throughout. Sprinkle green onions on top.