Is it permissible to give Zakat al-Mal in the form of food and goods instead of money, and would I be sinful for doing so?

What your friend did by paying food supplies instead of money for Zakat (definition), which is known as paying with value, is a matter of scholarly disagreement. The preponderant opinion is that it is not permissible unless the food supplies are more beneficial to the poor.

If the food supplies are more beneficial to the poor, such as in cases where it is difficult for them to obtain food, then what your friend did is correct and sufficient, although he should have sought your permission before acting. However, if the food supplies are not more beneficial to the poor, then what your friend did is not sufficient, and you must pay the Zakat again in cash.

You have the right to claim against the agent who acted without your permission, as he is considered to have transgressed. The obligation is not discharged until the money reaches those who are entitled to it.