Preheat oven to 400°F.
Cut the top off the head of garlic and remove any papery layers that come off easily. Place the head of garlic on a small square of aluminum foil and drizzle with the olive oil. Close the foil around the garlic and place on a baking sheet.
Roast the garlic for 25 minutes. Remove from the oven and allow the garlic to cool, enough to handle.
Meanwhile, layer the sliced vegetables in a lightly oiled cast iron skillet, starting with zucchini. Next layer the yellow squash, eggplant, ending with red pepper.
Squeeze the cloves of garlic into a small saucepan and mash with a fork. Pour in the cream, and add the onion and Italian seasoning and stir to combine. Heat over medium heat until the mixture starts to bubble.
Pour the cream mixture over the layered vegetables and top with the shredded parmesan cheese.
Cover the cast iron pan with aluminum foil and bake for 30 minutes. Remove the foil and continue to bake for 5 more minutes.
If desired, broil for 2-3 minutes, until the cheese is nicely browned.