In a large Dutch oven, heat 2 Tablespoons olive oil over medium heat. Add onion and garlic and sautée for 2-3 minutes until soft and fragrant. Add cauliflower florets and sautée for approximately 8 minutes.
Add soup stock, water, spinach, cashews, red pepper flakes, salt and pepper. Add more water if needed to cover all ingredients. Stir to combine. Bring to a boil, then reduce heat to low and simmer uncovered for 15-20 minutes or until the cauliflower is fork-tender. Remove from heat and let cool slightly.
While the soup simmers, preheat the oven to 350°F. Tear your bread slices into chunks and add to a spice grinder or small food processor. Pulse until coarsely ground. Transfer to a small baking sheet, drizzle with olive oil, garlic powder, salt and pepper. Toss to evenly coat. Bake for 10-12 minutes, or until slightly browned. Set aside.
Working in batches, transfer your slightly cooled soup to a blender and blend until smooth (you can also use an immersion blender). Pour into individual bowls, top with crispy breadcrumbs, and garnish with fresh dill, green onions, and an additional sprinkle of salt and pepper.