Mapster: mapping collection of object to dictionary of transformed objects

Question

Consider the following classes :

class B{
string FullName;
}
class A{
int Id;
string FirstName;
string LastName;
}
class AContainer{
  ICollection<A> aObjects; 
}
class BContainer{
  IDictionary<int,B> bObjects; 
}

the mapping logic :

AContainer aContainer = ...//get somehow
BContainer b = new BContainer{
bObjects = aContainer.aObjects.ToDictionary(a=>a.Id, a=>new B{ 
 FullName = @"{a.FirstName} {a.LastName}" }
)
}

How do I map such collection to keyed dictionary ? (I'm using Mapster.Tool to generate the interface implementation from the configuration)

Thanks