Heat oven safe skillet over medium heat, and add 1 tablespoon olive oil and the onions. Cook for about 5 minutes until the onions start to soften. Add garlic and stir for a minute or so.
Remove from heat and sprinkle ½ teaspoon of thyme.
If you do not have an oven safe skillet, transfer mixture to a baking dish. Spread the onion evenly on bottom of the pan, then layer potatoes, tomatoes, and squash in alternating order.
Drizzle with the remaining 2 tablespoons olive oil, salt,1/2 teaspoon thyme, and black pepper.
Cover with foil and bake for 35 minutes, until the potatoes are cooked through. Remove the foil, sprinkle the parmesan cheese and bake for another 20 minutes until golden brown. Enjoy
Recipe by To plate with love at https://toplatewithlove.com/vegetable-gratin/