Mix mustard, lemon, salt, sugar garlic salt and olive oil until you have a homogenic mixture.
Wash, rinse, and finely chop the leaves. Add leaves to mustard and mix well. You can put it in the fridge for a few minutes before pouring it over your favorite salad. Enjoy!
Note: I don't mention the quantity of salt, sugar, garlic salt, and leaves because this is to your taste. I used about 10 mint leaves, 10 oregano leaves and 5 basil leaves, because I really enjoy the flavor. And about 1/4 teaspoon of salt, the same amount of sugar and garlic salt. But, this is up to you!