Business lunches and dinners are quite common occurrences in Poland and form an important part of the relationship building cycle. Business breakfasts, on the other hand, are virtually unknown and it is not advisable to suggest this as a meeting forum.
It is difficult to give hard and fast advice around whether business should or should not be discussed over the meal. It is best to be led by your Polish counterpart on this and wait until they raise business matters before launching into a detailed debate on specific contract issues.
Any business entertaining is likely to be done in a restaurant, rather than at people’s homes and whoever invites usually pays. If you invite, ask for local advice for a suitable restaurant as quality is somewhat variable. (It is usual to tip around 10% at a restaurant.)
Poles like to entertain and be entertained, so be prepared for the possibility of a long evening with quite a lot of drinking. Beer and wine are being consumed in larger quantities but vodka remains a popular choice. Be careful if you have serious negotiations the following day!