Heat olive oil in a large pot over medium heat. Add leek and cook for 4–5 minutes until softened.
Add garlic and cook for 30 seconds, stirring.
Add cumin and stir for 30–60 seconds until fragrant.
Add pumpkin, green apple, red lentils, chickpeas, and chicken stock. Stir to combine.
Bring to the boil, then reduce to a steady simmer. Cook for 20–25 minutes, or until pumpkin and lentils are very soft.
Blend until smooth using a stick blender (or carefully transfer to a blender in batches).
Taste and season with salt and pepper. If the soup is too thick, loosen with a splash of hot water or extra stock.