PREPARE GRAINS
In a saucepan over high heat, bring quinoa and 2 cups water to a boil. Reduce heat to low, cover, and simmer for 20 minutes. Remove from heat and let cool; fluff quinoa with a fork.
SIMMER SOUP
In a stockpot over high heat, combine plant milk, vegetable broth, cauliflower, sweet potatoes, onions, curry powder, and cayenne pepper (if using). Cover and bring to a boil. Reduce heat to low and simmer until potatoes are tender, 15 minutes.
FINISH SOUP
Stir in kale and cook until wilted, 1 to 2 minutes. Season with salt and pepper to taste.
SERVE
Serve soup over quinoa. Top each bowl with scallions, then sprinkle with cashews and pepper flakes, if desired.