Pre-heat oven at 180˚C / 356˚F, fan bake. Line the base of a spring-form baking tin with baking paper and lightly grease the sides with olive oil
Place walnuts on an oven tray, toast until fragrant, then remove and roughly chop
Slice feijoas in half and scoop out the flesh, roughly chop, set aside with the walnuts for now
Sift all dry ingredients into a mixing bowl, stir to combine
Add oat milk and olive oil, fold through, taking care not to over mix
Add toasted walnuts and feijoas, fold through and transfer to the prepared cake tin
Bake for 25 minutes, then open up the oven quickly and cover the cake with foil, bake a further 10-15 minutes or until a skewer comes out clean (total cooking time of 35-40 minutes)
Remove from oven and let cool completely before removing from the cake tin and serving.