You will need:
Preheat the oven to 375 degrees. Coat a baking dish with olive oil cooking spray. Heat 1 tbsp of olive oil in a large skillet over medium heat. Once hot, add the onions and saute until translucent, about 8 minutes. Add the garlic and cook for another 60 seconds. Spread the onion mixture on the bottom of the greased baking dish.
Slice the potatoes, zucchini, squash mushrooms (if they are not pre-sliced) and tomatoes in 1/4 inch thick slices. Layer them alternately in the dish on top of the onions, fitting them tightly into a spiral, making only one layer. Season with sea salt, black pepper and dried thyme, to taste. Drizzle the last tablespoon of olive oil over the top.
Cover the dish with tin foil and bake for 35 minutes, or until the potatoes are tender. Uncover and sprinkle the Parmesan and feta cheeses on top and bake for another 25-30 minutes or until browned.