In a large stock pot or Dutch oven, add the olive oil and heat over medium-high heat. Add the diced onions and garlic and sauté for 5-7 minutes or until onions are nearly translucent.
While onions and garlic are cooking, place frozen cauliflower into a microwave safe bowl, with about 1/2 cup of water and microwave on high for 5 minutes to steam.
Place the steamed cauliflower, sauteed onions and garlic and half of the chicken broth into a blender. Blend on medium-high speed for 45-60 seconds or until creamy and smooth. Add puree back to stock pot.
In same microwave bowl, add the diced carrots and broccoli. Add 1/2 cup water and microwave on high for 5 minutes to steam.
Add the steamed broccoli and carrots to the cauliflower puree. Also add the shredded chicken, garlic salt, pepper and nutmeg. Add remaining chicken broth and stir. Heat over medium heat until soup comes to a low boil/simmer. Simmer for 5 minutes.
Stir in the shredded cheese and simmer for an additional 5 minutes.
Remove from heat and let cool for 5 minutes before ladling into bowls and serving. Top with additional shredded cheese, if desired.