In large saute pan, over med heat, add 1 TBSP olive oil and butter. When butter is melted, add diced onion and sauté until tender. Add garlic and sauté for another 2-3 minutes.
In large baking pan, pour onion/garlic mixture on bottom of pan.
Slice potatoes, zucchini, yellow squash, and tomatoes into 1/4" slices.
Arrange veggies on top of onion mixture.
Drizzle with 1 TBSP olive oil.
Sprinkle with salt, pepper, and thyme.
Cover with foil and bake at 375* for 45 minutes. Remove foil, top with parmesan cheese and bake for another 15-20 minutes.
**total baking time will vary on thickness of slices. Adjust as needed till fork tender.