In a glass jar or container with a tight fitting lid, measure and add the olive oil, balsamic vinegar, mustard, garlic and lemon juice. Shake well to combine and set aside.
Preheat your grill to 400℉ (or 200℃).
Thread potato halves onto metal skewers. Place skewers onto a rimmed metal baking pan and spray all sides with olive oil. Along with both sides of the cut red bell pepper and onion slices.
Once your gril has preheated, place down the skewers, onion slices and pepper. Close the grill and cook for about 12 to 15 minutes, turning halfway through. Adjust the heat to avoid burning. Once the bigger potatoes can easily be pierced by a fork, remove and let cool for about 5 minutes.
Meanwhile, chop the onions and red pepper.
Once the skewers are cool enough to handle, slide the potatoes off and into a mixing bowl. Add in the chopped pepper, onions and minced fresh parsley.
Pour in all of the dressing and season generously with kosher salt and freshly ground black pepper to taste. Taste test and adjust if necessary.
Toss well to combine before transferring to a serving dish and sprinkle with sliced green onions.
Serve warm or at room temperature.