Heat oil in a saucepan over medium heat. Add onion and leek; cook and stir until translucent, about 5 minutes. Stir in potato, broccoli, and cabbage. Reduce heat to medium-low and cook, stirring occasionally, until softened, 3 to 5 minutes.
Pour vegetable broth into the saucepan. Bring to a boil; reduce heat and simmer until vegetables are tender, about 15 minutes. Season with salt and pepper.