You mention both being vegetarian and having a soy sensitivity. IME Muslim/Hindu meals do not tend to include soy (generic "Asian Vegetarian" on other airlines often, but not always, includes tofu), so as at least the current menus are vegetarian, that's probably as high an assurance as you're going to get, especially for Mint where you can see the SPML menus (as cited upthread). The current vegetarian menu also appears to be soy free (unless it's lurking in a sauce or something).