consider using the processor to chop onions to your desired size
cook slowly in a large ( non-stick ?) pan until done to your liking
cool , and Vac w head room in a bag then freeze
you want a little head room so you cn cut open the bag , take out what you might need , then
re=seal that same bag
several times.
in the past Ive done this w mushrooms ( using the cuisinart , several pounds at a time )
and diced bacon never thought of doing the same w onions
but it might work . w onions you might want a version that is caramelized and one that is not.