In an 8-ounce or larger mason jar, combine the lemon juice, olive oil, mustard, garlic, oregano, salt, and black pepper. Stir well with a whisk or spoon. Or, secure the lid on the jar and shake well until the dressing looks emulsified.

This dressing tastes best if you can let it rest at least 10 minutes before serving, so the flavors can meld. Leftovers can be stored in an airtight container in the fridge for up to 5 days.