I puree anything I have available either in the fridge or freezer
eg frozen peas corn & carrot, spinach, broccoli, lentils, mushrooms, zuchinni, onion & capsicum (peppers)
Oh & you can also cook the spagetti in strained veg stock... can you see I have to sneak Veg in LOL
Whoever it was trying to hide from their dh... pureed (peeled) zuchinni (corgette) & pureed lentils actually hide pretty well in Mash Potato. I freeze cubes of both & when I make Mash I defrost them & add them in when I add milk & butter... dh actually thinks it tastes better (not realising I did it until eating My Dad's Mash & saying how bland my Dad's was

)