Put the lemon juice, oregano, garlic, salt, and pepper into a medium bowl and stir together. Vigorously whisk in the olive oil in a stream.
Alternatively, you can add all of the ingredients to a salad dressing shaker or a jar with a lid and shake vigorously until combined.
Notes
Dried oregano is going to give this dressing a Greek vibe. However, you can use other dried herbs like rosemary, basil, or Italian seasoning. If you would like to use fresh herbs, triple the amount.
You can also substitute minced shallot or onion for the garlic.
Use high-quality extra virgin olive oil since this is one of the main ingredients and is not being cooked. Use something that you enjoy the taste of on its own.
If you want a sweeter, less acidic dressing, you can add a small amount of sugar or honey.
Shake or whisk the dressing immediately before serving so that all of the ingredients are evenly distributed when pouring. When this dressing sits, the heavy stuff goes to the bottom.
Store this dressing covered in the fridge. The dressing will solidify slightly when cold so when you are ready to use it, bring it to room temperature. You can either set it on the counter ahead of time or place it in a bowl of warm water for a few minutes.