Place cashews in a bowl and add 2 cups HOT water. Let soak while you prepare remainder of recipe.
Heat oil in a large soup pot or Dutch oven with a fitted lid over medium. Add onions and celery; cook 5 minutes, until softened. Add potatoes, garlic, oregano, salt, pepper, thyme, and rosemary; cook 5 more minutes, stirring often. Stir in frozen vegetables and chickpeas.
Add broth and bring mixture to a boil, scrapping up any browned bits on the bottom of pan. Reduce heat to medium-low and simmer, covered, 20 to 25 minutes, until potatoes are tender.
Transfer cashews and soaking liquid to a blender and blend on HIGH until smooth (texture should resemble cashew milk). Pour cashew mixture into soup and simmer over medium-low, uncovered, until soup starts to thicken, about 8 to 10 minutes.
Remove bare thyme stems and adjust seasonings as needed. Ladle soup into bowls and add garnishes of choice (more fresh herbs, crushed crackers, croutons, etc.)