Eating at Subway

Question

Dear Rabbi Description of Subway Tuna Salad Sandwich Tuna salad made with light mayonnaise. Dolphin-safe tuna and creamy light mayonnaise is lovingly blended together to make one of the world’s favorite comfort foods. The Subway Tuna sub is available with your choice of fresh vegetables and condiments served on freshly baked bread. Fresh Value Meals include chips and a 21ounce soft drink--or swap your chips for two cookies. My question is: If I bring my own kosher bread to Subway and ask them to prepare the above meal for me, if this OK? They have agreed to do this if it will allow me to be their customer.