In a large pot over medium heat, add the olive oil, white/light green scallions, and ¼ teaspoon salt. Cook until softened, about 2 minutes, stirring occasionally. Stir in the potatoes, onion powder, garlic powder, black pepper, and remaining 1 ½ teaspoons salt, stirring constantly for about 30 seconds.
Stir in the chickpeas, water, and mustard. Increase the heat to high to bring to a boil. Give it a stir, then reduce the heat down to medium to maintain a rapid simmer for 20 minutes, stirring halfway through
Remove about 2 cups of the soup, making sure to get potatoes and chickpeas in there to help thicken the soup, and transfer to a high-speed blender. Blend until smooth, then pour back into the pot. Stir in the greens and cook until wilted, about 1-2 minutes. Stir in the vinegar. Taste and add more salt or vinegar, if needed (this a very simple soup and both potatoes and beans need lots of salt to bring out their flavor).
Serve topped with yogurt or sour cream, lots of green scallions, crumbled potato chips (if using), and black pepper.