Start by finely dicing the onion and red bell pepper. Then chop the fresh parsley and basil. You’ll find options in the recipe for how to make this with dried herbs as well.
Whisk together the vinegar, Dijon mustard, onion, dried oregano, and bell pepper in a mixing bowl. If you’re using the blender, I like to add the bell pepper at the end as listed in the recipe below.
Next, slowly whisk in the oil until completely emulsified, then season to taste with sea salt, pepper, and chopped herbs. Or you can make this in a blender.