Whisk. In a mixing bowl, combine the lemon juice, Dijon, garlic, oregano, and a big dash of salt and pepper (1/2 to 3/4 teaspoon each).
Incorporate the oil. Whisk and while whisking, drizzle the extra virgin olive oil. Continue to whisk until fully emulsified.
Use or store. Taste and adjust seasoning to your liking. Store, covered in your refrigerator, for up to 1 week. Simply give it a good whisk to reincorporate the oil.