Combine Ingredients: In a small mixing bowl, whisk together the olive oil, lemon juice, and minced garlic (if using) until well blended.
Season: Add the oregano, Dijon mustard (if using), salt, and black pepper. Whisk until emulsified and slightly thickened.
Taste and Adjust: Adjust lemon, salt, or garlic to your preference. Add more lemon juice for tang or mustard for creaminess.
Serve: Use immediately on salads, grilled meats, vegetables, or as a dipping sauce.
Store: Store in a sealed container in the fridge for up to 1 week. Shake or whisk before using.