For the ratatouille, finely chop the onion and garlic. Cut eggplant, zucchini, tomatoes and feta into bite-sized pieces.
In a pot, fry the onion in oil. Fry the garlic and add the flour to make a roux. Add the vegetable soup and bring to a boil.
Add eggplant and simmer for 15 minutes. Add zucchini and cook for another 5 minutes. Add tomatoes and cook for another 5 minutes.
Remove ratatouille from heat and stir in feta pieces. Season with parsley and salt and serve.