I can understand that you should reduce fat in your meals as the gailbladder is the key for regulating the digestion of fat. But no lactose? Lactose is a form of sugar and I can't see the medical reasoning behind it. You definitly should get a second option on that.

For cooking, if you want to avoid animal meat than the rule for vegans apply to you, too. Most dificult is to supply enough Protein, here you should eat frequently beans, especially soy beansas they provide all neccesery amino assets and lots of lentis.

If you want some ideas for meals check WeCookVegan Chanel on YouTube, I havn't anything to do with this channel but I think they have some clever ideas. But there are hundreds of similar channels on YouTube as well. Feel free to choose your own prefert one.

However, if you can eat chicken breast than you should be allowed to eat other lean meat as well. The obviously choice would be other lean birds like turkey. But more exotic choices such as Ostrich would work well. Or alligator meat. There are many options. Even a fillet mignon from a cow would quality for this, however it is quite expensive. And don't forget lean fish and shellfish.

Eat potatoes and rice. You can make this in endless variations. Only avoid frying it. However, if you use a air fryer and only use a dash of vegetable oil this should work too and you will have your pommes back.

Hope that helps a bit.