Add the chopped onion and celery to a 4-quart pot with 3-4 tablespoons of water and cook on medium heat, stirring, until the onions have softened (about 5-7 minutes).
Add the garlic, thyme, and red pepper flakes and cook for another minute until fragrant.
Add the potato and broth and bring to a boil. Once boiling, reduce to a simmer and partially cover the pot. Simmer for 15-20 minutes or until the potatoes are just tender.
While the potatoes are cooking add the miso, nutritional yeast, tahini and lemon juice to a small-medium sized glass bowl. Add ¼ cup of the broth from the pot and whisk together until no lumps remain and the mixture is smooth. Set aside.
When the potatoes are just about tender add the broccoli and chickpeas to the pot and continue to simmer with the cover off for about 3-4 minutes or until the broccoli is bright green and tender. Then add in the miso/broth mixture and stir to combine. The soup will lighten in color. Here you could also blend half the soup to get a thicker consistency. Taste and re-season.
Divide the soup into bowls and garnish with nuts or seeds, more red pepper flakes, and baby greens. Add hot sauce if you like it hot!