A seige means the borders are closed. The current situation, for at least 6 months now is that Israel is letting food trucks through the border, more and more every day.

A problem exists for that last mile inside Gaza where no one wants to distribute it because militants will straight up beat truck drivers with sticks to steal the trucks and the food.

You'd think the UN would step in and do something but so far they mostly just sit on their hands bleating.

So to summarize: there are huge piles of food just inside the Gaza border that are not being distributed efficiently/at all.

I also want to point out that it's not in Israel's best interest for there to be food shortages inside Gaza. The first people who will be starved are the hostages, so Israel wants to flood the strip with so much food that some trickles down to her citizens held there against their will.