Add the vegetable stock, barley, tomatoes (including juice) and all long-cooking vegetables. Hold off on the zucchini and any short-cooking vegetables (such as frozen peas if you aren't using fresh). Add seasoning to taste.
Bring to a boil. Once boiling, reduce to a simmer and cover.
After it simmers for about 30 minutes, add the short-cooking vegetables. Taste the broth and adjust seasonings if needed.
Bring to a simmer again and cover. Simmer for about 1 hour (or longer if desired). If it gets too thick, add more broth or water.