Peel and dice the sweet potato and slice the fish into 2cm chunks. Place the sweet potato and fish into a medium pan, add the milk to just cover the fish and bring to the boil over a high heat.
Once boiling, reduce to a simmer and cook for 5 to 8 minutes, or until the potatoes are tender, adding the peas for the last couple of minutes. Drain and mash together, reserving a splash of the poaching milk.
Remove the amount needed for your baby, adding some of the reserved milk to loosen to the desired consistency.
For adults and toddlers, crack 1 egg into the remaining mash, and finely grate in the lemon zest. Season lightly with sea salt and black pepper, and stir well to combine, then leave in the fridge to cool completely.
Meanwhile, whisk the remaining egg and a pinch of sea salt in a shallow bowl. Place the oats or Ryvita crackers into a blender and whiz until fine, then tip into another shallow bowl.
Scoop out 1 tablespoon of the fishcake mixture and shape into a small patty. Dip the patty into the egg, letting any excess egg drip off, then cover in the breadcrumbs.
Place onto a lined baking tray, and repeat with the remaining ingredients – you should end up with around 12 patties.
Drizzle with a little oil then bake in the oven for 15 to 20 minutes, or until golden, turning halfway, then leave to cool slightly. Delicious served with seasonal greens, or a fresh green salad.