Introducing solids is known as complementary feeding or weaning and it is the introduction of foods which complement your babies usual milk — rather than replacing it. (babease.co)
You can use soymilk for just about anything you put usual milk in. (mealpreponfleek.com)
For younger babies (7 - 8 months) I would recommend using the ingredients (without making the fishcakes for baby), pureeing, mixing with baby's usual milk and serving with the vegetables as finger food. (anniesdorsetkitchen.com)