Preheat a gas or charcoal grill to medium high heat.
In a medium bowl, combine the cubed California sweetpotatoes, olive oil, salt and pepper and toss to combine.
Tear 4 large sheets of aluminum foil, about 16 inches long each. Divide the sweetpotato mixture amongst the 4 sheets of aluminum foil and fold the sides up on both ends so you create a securely wrapped parcel for the potatoes.
Place the 4 parcels on the grill and cover. Let the potatoes cook for about 7-8 minutes on each side. When flipping the potato parcels, be sure to use a pair of tongs and a spatula so the parcels stay intact.
Once the sweetpotatoes are fully cooked and fork tender, carefully remove the sweetpotato parcels from the grill and transfer the sweetpotatoes to a bowl.
Brush the cob on the cob with olive oil and transfer to the grill. Cook until slightly blackened. Remove the corn from the kernel and add to the bowl of sweetpotatoes. Add the feta cheese and fresh dill and toss to combine.
Whisk together the ingredients for the lemon vinaigrette and drizzle a little bit on top of the sweetpotatoes, tasting and adding more if needed. Adjust salt and pepper and serve.