In a large, non-aluminum bowl, combine red wine vinegar, green onion, minced garlic, sugar, sweet Hungarian paprika, dry mustard, dried tarragon, dried thyme, dried oregano, salt, and fresh ground pepper.

Whisk in vegetable oil in a thin stream until well combined.

Add thinly sliced red onions to the bowl and toss well to coat.

Cover the bowl tightly.

Refrigerate for at least 2 hours, or up to 7 days, before serving. The longer they marinate, the more flavorful they become.