Place the cashews in a small bowl and cover with water. Set aside.
Place the onions, garlic, vegetable stock, crushed tomatoes, sun-dried tomatoes, tomato paste, Italian seasoning, salt, and honey (if using) into the base of a slow cooker, stirring to combine.
Cover and cook on high for 4 hours or low for 6 hours.
When the soup is finished cooking, drain and rinse the cashews. Place the soaked cashews into the slow cooker, stirring to combine.
Using an immersion blender, blend the soup until well combined and very smooth, about 2 minutes. If you don’t have an immersion blender, carefully ladle the cooked tomato mixture into a blender, working in batches. Make sure the lid is on tightly, cover with a towel, and blend until well combined and very smooth.
Serve with toppings, if desired.