The customer asked for no cheese on their salad. They are lactose intolerant and the cheese would make them sick. The server accidentally hit the “extra cheese” button instead of the “no cheese” button.

Apologize to the customer to show that you understand the mistake you made and that you acknowledge their complaint. Then, find a solution to the problem. In this case, you can take back the salad with cheese (unless they want to keep it to give to someone else). Make a new salad with no cheese and give it to them. Make sure that they're satisfied with their new salad by following up with them. You can also send them a hand-written note with a gift card or some kind of exclusive offer for them (e.g., a discount on their next order, free item(s), etc.) to show your sincerity.

answer; capital structure decision;