I cook a lot of vegan soups for my wife and I've come to some tips after too many watery soups.
- Fry the onions. Heat up the soup pot and throw a bunch of onions in the bottom and fry them until they brown. This adds an umami flavor to the soup. For rescuing a soup like this, chop them very fine, fry and simmer them in the soup for a while.
- Use a can of dark beer as your first cup of water. This also increases the umami flavor as it cooks down. With the chicken stock, I'd use a lager if you need to add more liquid to the soup, then simmer for a while to let the flavors blend.
- Add a can of tomato paste or diced tomatoes as part of your broth. A long simmer with tomatoes adds the acidity, adds body to the broth and more of that crucial umami flavor. Tomato paste has a tendency to give a 'beefier' flavor, so omit for chicken. Consider instead diced tomatoes or a roux.
- Oxo (or other) vegetable broth cubes. For a large pot of soup, add 3 or 4. This is a bit of a cheat around creating a mirepoix blend (homemade veg broth is better) but it could rescue your veg soup.
I've also had luck with thickening the soup with a roux, mix up your flour and water, pour it into the pan and stir while the flour browns. Stir it into your soup and use some spices, Rosemary, thyme, parsley, pepper, paprika,
Worchestershire Worcestershire sauce, hot sauce (I'd suggest something with flavor like Tiger Sauce) to liven up the soup.
Because you've got the more delicate veggies like the kale and the zucchini already in the water, I'd focus on thickening the broth or increasing the flavor of the broth.