1. Whisk red wine vinegar, Dijon mustard, oregano, garlic, salt, and black pepper together in a small bowl.
2. Slowly pour olive oil into the vinegar mixture while whisking. Then, whisk the lemon juice into the mixture.
3. Pour the dressing into a seal-able jar or bottle, seal it, and shake until the dressing is emulsified.
4. Store it in an airtight jar or bottle. This dressing lasts about 2 weeks sealed and in the refrigerator.