No, I am not going to tell you anything, it is an ancient Asian peoples secret.
I will tell you this.
1. There is a pate spread used in Banh Mi, it is pretty much one key to a successful replica. Every cook has their own recipe. It is however, possible to simply buy some Pate de Campange and mash it up into a spread.
2. You can use just about any meat, but, remember that it is a street food in origin, and is great with grilled meat with a nice sweet/savory flavor. Any meat works, but, chicken and pork are going to be the most likely traditional meat.
3. The bun, and this is the hard part, should be made with a mix of rice and wheat flour to get a thin crisp crust and a very light tender crumb. Overall the bread is very similar to a small baguette. Although most store bought baguettes in this country suffice, they are far from ideal.
4. The bread is generally not toasted, the vegetables are cold and the meat is usually hot. There is no dressing, although mustard is sometimes used. I actually like a nice grainy mustard on mine. No mayo! The pickled vegetables provide the moisture the sandwich needs.
As for meat, I would say that while I have offered many recipes for Asian-ish meat for grilling, my current post on
Viet-inspired pork would work great. Hmm, that pretty much covers the secrets, dang, he pried them out of me