Toss potato slices, zucchini slices and leek halves in olive oil until evenly coated. Season with salt and pepper. Place vegetables in an even layer directly on the grill. If slices are small, use a vegetable basket to avoid pieces slipping between the grates.
Grill for 2 minutes per side or until cooked through. Remove from heat and set aside. When leeks are cool enough to touch, thinly slice.
Meanwhile, roll out pizza dough on a floured cookie sheet to the desired thickness. Flip the cookie sheet to place the dough directly on the grill grate.
Remove the cookie sheet and close the grill. Cook until the bottom is charred, 3-5 minutes.
Using tongs or a grill spatula flip the dough over. Spread with garlic cloves and leeks.
Sprinkle with ½ cheese.
Layer slices of potato and zucchini evenly over the top of the crust.
Top with remaining cheese.
Close the grill lid and cook until cheese melts and the dough is fully cooked through.