Now you might be wondering what a Tian is, right? Wikipedia states that a Tian is an earthenware vessel that is used for cooking and serving and it is also the name of the dish prepared in it. Over time, the classic cone shaped vessel from the Provence region in France has changed as well as the dish itself. In the 18th Century a Tian was typically a lean stew, where the modern Tian is a dish cooked with no added liquid and generally made with vegetables alone, more commonly called a gratin in the United States.
With zucchini and tomatoes a plenty in the garden I thought it would be a colorful dish. It was prettier being assembled than after cooking, but it still tasted great.
Heat 2 Tb of olive oil in a large pan and cook 1 1/2 cups of sliced onions with a teaspoon of salt for 10-15 minutes or until lightly browned, stirring occasionally. Add 2 minced garlic cloves and cook for 30 seconds. Place all of the onions on the bottom of a small gratin dish and then start making layers.
I placed two rows of zucchini slices side by side and covered each row with brightly colored tomatoes, then a light sprinkle of Italian seasoning, and 1/4 cup of shredded Gruyere cheese.
Again with sliced zucchini, more tomatoes, followed by the seasonings and a final layer of zucchini, salt and pepper. Cover the dish with foil and bake in a 375 oven for 30 minutes.
Remove the foil, sprinkle zucchini with another 1/4 cup of shredded Gruyere and continue to bake until bubbly and lightly browned on top, about 20-30 minutes.