In a bowl, mix the Sour cream, minced garlic, and lemon juice. Set aside in the refrigerator till we are ready to make the sandwiches
Boil the potatoes for 10 Minutes until tender. Once done, drain the potatoes
Preheat the grill for high heat.
Brush vegetables with olive oil on each side. Place bell peppers and zucchini closest to the middle of the grill, and set onion and squash pieces around them. Cook for about 3 minutes, turn, and cook for another 3 minutes. The peppers may take a bit longer. Remove from grill, and set aside.
Spread some of the 1/3rd of the cream mixture on one side of the bread, and sprinkle each one with feta cheese. Place the grilled cheese side up. This will warm the bread, and slightly melt the cheese. Watch carefully so the bottoms don't burn. Remove from grill.
Layer with the vegetables. Place two pieces of Squash, then two pieces of Zucchini, 3-4 pieces of Onion rings, and 2 pieces red bell pepper.
For the potato salad dressing, whisk together the canola oil, vinegar, Mustard Sauce, celery salt, Black pepper.
Toss the potatoes with half the dressing. Let it sit for 10 minutes. Then toss the potatoes with the remaining dressing.
Enjoy as open-faced grilled sandwiches