Put the plum flesh, lemon juice, date syrup and vanilla in a small pan and cook over low heat until you get a sticky, jam-like mixture. Let it cool.
Preheat the oven to 180°C.
Line a medium bread tin with paper basket or prepare a silicon loaf mould.
In a bowl, mash the bananas, then add the flour, baking powder, oats, spices and milk. Combine gently.
Add more oats if it’s too thin, or add more milk if’s too thick - you should have a thick batter, not a dough.
Fold in the chopped nuts.
Spoon half the mixture into the prepared tins then spread some plum jam over it (but don’t go right to the edges, otherwise the jam will escape during baking).
Spoon the remaining batter over the jam, spreading it out evenly.
Bake for about 35-45 minutes until golden.
Let it cool completely in the tin, then cut it into 1cm thick slices.