countries.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApp4
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Begin");

            var countries = new List<string>() { "Dominican Republic", "Argentina", "Mexico" };

            var stringbuilder = new StringBuilder();

            foreach (var countryName in countries)
            {
                var guid = Guid.NewGuid();
                var country = new Country() { Id = guid, Name = countryName };
                stringbuilder.AppendLine(country.GenerateHasData());
            }

            // Use a breakpoint to examine the result variable and take all of the generated code 
            var result = stringbuilder.ToString();

            Console.WriteLine("Fin");
        }

    }

    public class Country
    {
        public Guid Id { get; set; }
        public string Name { get; set; }

        public string GenerateHasData()
        {
            return @$"modelBuilder.Entity<Country>().HasData(
            new Country(){{
                 Id = ""{Id}"",
                Name = ""{Name}""
                }}
            );";
        }

    }
}