2 tablespoons olive oil
1 medium yellow onion, finely diced
4 cloves garlic (or more, if you like!), very thinly sliced
2 medium carrots, very thinly sliced
1 celery stalk, very thinly sliced
1 cup green lentils, French Le Puy if you can find them
1 1/2 tablespoons Dijon mustard
4 teaspoons red wine vinegar
1 1/2 teaspoons kosher salt, plus more to taste
1/2 teaspoon freshly-ground black pepper, plus more to taste
1/4 cup chopped Italian parsley, to top (optional)
fried egg, to top (optional)