Heat olive oil in a large saucepan over medium heat, then add the onions and cook until soft and translucent, about 5 minutes. Stir in the butternut squash, stock, and water and bring to a simmer. Cook until squash is tender, about 15 minutes.
Remove soup from heat and puree until completely smooth using a handheld or regular blender. Once well-blended, stir in the half-and-half and seasoning mix; bring to a simmer and cook for 5 more minutes.
Ladle the soup in bowls and serve hot. (For an extra pop of texture and flavor, garnish the soup with toasted croutons or crumbled bacon.)