In a medium pot, heat the olive oil over medium heat. When the oil is hot, add the leeks or shallots, when they are lightly golden, add the carrots and celery, and a pinch of salt, and cook until it has wilted, about 6 minutes.
Add the tomatoes, slosh out the can with a bit of water, and add that to the pot along with the cucumbers, basil, orange zest and juice, salt, celery seeds, black pepper, and red pepper flakes. Set the lid ajar, and simmer until the soup is flavorful and the vegetables are very soft, about 35 to 40 minutes.
Let cool slightly, then remove the orange peel, add the vegan yogurt, and blend the soup.
Transfer to a bowl or pitcher, and refrigerate until very cold, at least 3 hours.
Taste, and season for salt again once the soup is chilled
Serve it cold on a cold bowl, then garnish with some extra minced fresh tomatoes or roasted cherry tomatoes, minced cucumbers, and basil leaves, and drizzle with some extra yogurt and extra olive oil.
😎 IMPORTANT TIP: You can add the cucumbers raw, right before blending the soup, it tastes even more summery and fresh this way.