Preheat the grill to high.
Add the potatoes to a large pot of boiling salted water and cook for 8 minutes or until just before al dente.
Strain the potatoes and add them to a bowl and toss with 2 tablespoons of olive oil and add them to the grill, to slightly char and finish cooking.
While the potatoes are cooking, coat the onion slices in the remaining oil and add them to the grill to roast.
Once the potatoes are slightly charred and cooked through, remove them from the grill along with the onions and chill.
Next add the bacon strips to a cooler part of the grill and cook until crispy. Note the bacon will cause a lot of flames so constantly be turning them and moving them. The bacon will also cook very fast.
Once the bacon is cooked, remove and chop.
In a large bowl whisk together the mayonnaise, mustard and apple cider vinegar until combined and add in the potatoes and onions once cool along with the bacon, dill, green onions, salt and pepper and toss and chill. Serve cold.