While there are vegetarian alternatives out there, The answer is simple: use shiitake mushrooms. Mushrooms have a natural, intense flavor – and the same goes for the dried version – so they're a great alternative to meat in plenty of dishes, particularly those that include bacon, such as this carbonara.  In fact, most people will barely realize the difference, especially if you use shiitake mushrooms in addition to the regular bacon. If your soup already has mushrooms, you could add tofu or veggie bacon. You could also add seitan which is made from wheat gluten and has an extremely chewy texture.