Slice onion into thin strips and place in a saute pan over medium heat with a couple tablespoons of the oil. Saute until translucent. Add whole garlic cloves and red wine and simmer for 10-15 minutes.
Meanwhile, in another pan, heat another couple tablespoons of oil over medium high and add in whole mushrooms. Saute in batches until browning and beginning to release their juices.
Slice or break up canned tomatoes and add to wine and onion mixture, along with their juices. Add herbs and spices, and browned mushrooms and continue to simmer for another 5 minutes. Add vinegar and salt and any remaining olive oil, taste to adjust seasoning and set aside to cool. Store in a jar in the fridge and enjoy! Best after marinated for a day.