Heat about 2 teaspoons of olive oil in a large skillet and add sausage. Cook until browned. Drain if necessary, and set aside.
In a large pot, heat about a tablespoon of olive oil over medium-high heat. Add onion, garlic and cook until onions are softened and translucent, about 5 minutes.
Add diced squash, sage and red pepper flakes and cook for another 5 minutes.
Pour in chicken broth and water and stir. Bring to boil and allow to simmer for about 10 minutes or until the squash is very tender and easily pierced with a fork.
Using an immersion blender, puree the mixture until completely smooth. Alternatively, you can pour the mixture into a blender and blend in batches -- just be careful as blending hot liquids can cause the lid to pop right off! {Not that it's ever happened to me or anything...}
Add diced red bell pepper and simmer until the pepper is tender, about 4-6 minutes. {You can skip the simmering if you're using a roasted red pepper as it is already soft.}
Stir in half and half {or milk alternative}, spinach and cooked sausage and heat until the spinach is just wilted.
Season with salt and pepper to taste. {I didn't add any extra salt because the sausage is salty enough.}