Dice the onion and mince the garlic. Add the olive oil, onion, and garlic to a large soup pot and begin to sauté over medium heat.
While the onion and garlic are sautéing, dice the celery, then add it to the pot and continue to sauté. As the celery, onion, and garlic are sautéing, peel and chop the carrots into half rounds. Add the carrots to the pot and continue to sauté.
As the onion, garlic, celery, and carrots are sautéing, peel and cube the potatoes into 3/4 to 1-inch pieces. Add the cubed potatoes to the pot along with the lentils, rosemary, thyme, Dijon, soy sauce, brown sugar, and vegetable broth.