Heat oil in a large saucepan over medium heat. Add mushrooms, leek, salt, red pepper flakes, and pepper; cook and stir until mushrooms are soft, 5 to 10 minutes.
Stir crushed tomatoes, creme fraiche, carrots, red lentils, vegetable broth, and sambal oelek into the saucepan. Bring to a gentle simmer. Cover and cook, stirring occasionally, until flavors combine, about 20 minutes.
