I had a food crisis on a fairly large fort of mine recently that was basically the result of me not paying close enough attention to my food industry.
You probably know all this, but I'm going to run through the food sources available to you and the processes involved:
Plump Helmets: planted, harvested, eaten. You can also cook or brew them, of course.
Quarry Bushes: must be planted and harvested, then processed to a bag by a thresher (plant processing labour) at a farmer's workshop, then cooked at a kitchen (uses the "cooking labour").
Meat: Dead, butcherable animals can be butchered or live, tame animas can be designated for slaughter. Both requires the butcher's shop and a dwarf with the butchery labour enabled. The meat can be cooked or eaten raw; the fat produced by a butcher's shop can be processed into tallow at a Kitchen, with the Cooking labour, then cooked. Hunting is a good way to provide food IF you don't have dangerous animals; otherwise, hunters tend to get killed.
Fish must be caught and cleaned at a fishery, by a dwarf with the fishcleaning labour.
So, now you need to figure out why none of this is happening quickly enough. The number of plump helmets you have designated, with the number of farmers, should be enough to feed your fortress all on its own. Keep an eye growers are doing their jobs and not getting distracted. The same goes for all the other dwarves involved in food production. Keep an eye all the relevant workshops as well, to see if the job is available and if that little green "a" is there; if the job isn't getting done, find out why.
To sustain your fortress in the meantime, find something your dwarves can eat NOW. Animals that can be butchered, seeds (especially outdoor seeds, if you aren't interested in farming them) can be cooked. If you have raw fish, make sure they get prepared.