Saute onion in hot oil in a Dutch oven over medium heat for 6-8 minutes, or until tender. Add garlic and cook 1 minute more. Stir in tomatoes and next 8 ingredients. Bring to a boil; reduce heat to low and simmer, stirring occasionally, 15 minutes.
Stir in spinach and chopped parsley; cook 5 minutes. Top with crumbled feta cheese, if desired.