Set a block when something happens

Solution 1:

All you need is to tag the player who has the hunger 0 and not act on it. So you would:

• Execute the Say command as a not tagged and hungry player
• Execute the tag add
• Remove the tag if he isn't hungry

And they would look like something along the lines of:

/execute as @a[scores={hunger=0},tag=!hungry] run say you cant do that anymore
/execute as @a[scores={hunger=0}] run tag @s add hungry
/execute as @a[scores={hunger=1..}] run tag @s remove hungry

the ! in front of hungry will negate the tag, so it would be read as "Not hungry"

Also, not that tellraw would be more appropriate here as say will be shown to all players.