sudo chmod 700 /mypool/mydataset
sudo chown user:group /mypool/mydataset

# for "username"
sudo setfacl -m u:username:rwx /mypool/mydataset

# for "user"
sudo zfs allow user create,snapshot mypool/mydataset

# view perms
sudo zfs allow mypool/mydataset

# remove perms for "user"
sudo zfs unallow user create,snapshot mypool/mydataset