I got an assembly with many concrete types that implement IHandler, such as the following:
IHandler
public class MoveCustomerHandler : IH
In a similar style to Jim's answer but taking advantage of AsClosedTypesOf:
AsClosedTypesOf
Assembly[] assemblies = GetYourAssemblies(); builder.RegisterAssemblyTypes(assemblies) .AsClosedTypesOf(typeof(IHandler<>));