Place 12 pieces of seitan on a baking sheet (6 per sandwich) and cook in the oven on 375 for 10-15 min or until crispy
While the seitan is cooking, prep your mayo. Combine 1 cup of mayo, chopped basil, lemon juice, salt and pepper. Allow to chill in fridge until you are ready to build your sandwich
Slice tomato and prep lettuce, set aside
When the seitan is finished, remove from oven and start building your sandwich
I like this sandwich grilled using a grill pan, but if you don't have one, toasted bread works fine
Spread remaining mayo on the outside of your bread and place it face down on the grill pan on medium to low heat. The mayo gives you a nice caramelized, crispy outer crust.
Build your sandwich starting with spreading the lemon basil mayo from edge to edge.
Then add your lettuce, 6 pieces of seitan for each sandwich, and top with tomato.
Spread more lemon basil mayo on the top piece of bread, and spread mayo on the outside of the bread.
Grill until each side is browned up and has grill marks.