It is very unlikely your pullets will over eat.
Are you feeding them growers or layers? If they are still so far from laying they should be on a growers pellet which is higher in protein than the layers. At this stage they also don't need the extra calcium which is also present in the layers.
If you pullets free range in your garden, or are in a run they should have free access to their pellets all day. This is because chickens are grazers like cows or horses, and do not eat "meals" like cats or dogs.
The only type of chickens which are likely to over eat are commercial broilers, and this is because they have been genetically programmed to eat and eat and eat to enable them to put on as much muscle mass as possible in their short lives. Home reared broilers should have thier feed restricted, but even then it is usually on a 12 hour on / 12 hour off schedule.
Broccoli should be fine to give your pullets, if they like it
If they are in a run with little access to grass, you should give them some greens every day.