Preheat oven to 350 degrees.
Add pure olive oil and onions to large skillet on MEDIUM. Cook, stirring occasionally, about 15 min, until soft but not browned. Season to taste with salt and pepper.
Arrange onions in single even layer in 13x9x2 inch casserole dish; top with thyme. Alternate slices of yellow squash, zucchini, and eggplant over onions to create 3 slightly overlapping rows of veggies lengthwise in the pan. Sprinkle with salt and pepper. Dollop with tomato sauce; spread with spatula to cover vegetables.
Bake 20 min. Remove from oven; top with dollops of ricotta. Return to oven; cook 30 min. Drizzle with olive oil.
give credit: betsy