Heat the oil in a large Dutch oven over medium heat.
Add garlic, onion, Greek seasoning and lemon zest; cook until onions have softened and spices are fragrant (5 to 7 minutes).
Add next 8 ingredients (bell pepper through tomato sauce). Bring mixture to a boil (stirring constantly) then reduce heat, cover and cook for 30 minutes to 1 hour until mushrooms are tender.
Serve topped with crumbled Feta, if desired, and enjoy!