In a large skillet heat 2 tablespoons of olive oil and add onion, oregano, and thyme. Sauté over medium heat until onions are translucent (about 10 minutes). Remove and place in a medium size bowl. In the same skillet, heat 2 tablespoons of olive oil. Add zucchini and mushrooms and saute until most of the liquid has evaporated (about 8 minutes). Turn heat off. Before removing from the skillet, incorporate the baby spinach into zucchini and mushroom saute, allowing the warmth to slightly wilt spinach. Transfer saute to the same bowl as the onion. Add feta, split farro, beaten eggs, yogurt, and lemon juice. Stir until all ingredients are combined. Add salt and pepper to taste.
Turn oven on to 375 degrees.
Combine melted butter and remaining olive oil. Lightly grease a 9″ x 13″ inch baking pan. Unwrap Filo from packaging and lay out lengthwise. With kitchen scissors, cut sheets in half. Once cut, filo should fit perfectly into a 9″x 13″ pan. Place one (1/2) sheet of filo into the pan at a time and brush the top lightly with olive oil/butter. Layer 1/3rd of the total number of sheets (about 18-20 sheets), brushing oil/butter mixture in between each sheet. Add 1/2 of the vegetable filling, spreading it evenly across the pan and gently pushing it down with a spoon (or your hands) to create a even layer. Repeat the layering process with 1/3rd of the filo dough, brushing oil/butter in between sheets. Add remaining vegetables.. Finish pie by adding the final 1/3rd of the filo sheets. Brush the top sheet generously with butter/oil blend.