Heat oil in a large pot. Stir in the onions (and cubed russet potatoes, if using these). Season with curry powder, red pepper flakes, and salt. Cook and stir on medium heat until onion (and potatoes) are tender.
Stir in the sliced zucchini, and cook till tender.
Pour in the chicken stock and bring to a boil, then add the instant potatoes (if using). Cover and reduce heat to low. Simmer for approximately 20 minutes.
Remove soup pot from heat. Use a hand mixer OR transfer in batches to a food processor or a blender, and blend till almost smooth. Transfer hot soup to serving bowls and garnish with croutons, if desired. Enjoy!
Curried Zucchini Soup https://www.thegratefulgirlcooks.com/curried-zucchini-soup/