Here's my easy way of making banh mi. It's easy to make in Mexico because mung bean sprouts are easy to find, and everything else is pretty basic.
This is a really simple recipe. You can toast the bread if you want to, or spread on pate, butter, or mayo, or sprinkle on some soy sauce. You can add cucumber and cilantro if you'd like. I use bolillos here, obviously, but in the US I could buy Vietnamese baguettes, or just get some good rolls. I don't care.
In addition to the bread, you need vegetables and protein.
For the vegetables, I just dump some bean sprouts and grated carrots in a bowl with vinegar, salt, water, and cayenne. You can make it as vinegary as you like. Let that sit for a few hours.
I usually do pork, tofu, and eggs for the protein. I scramble some eggs (I don't do much with these since the youngest likes the egg sandwiches best, but you could add garlic and shallots, or some chiles, or whatever), and stir-fry the firmest tofu I can find (I haven't seen pressed tofu here, so I use extra firm) with some vinegar, soy sauce, or sesame oil. I cut the tofu into long, thin slices. You can use any strongly-flavored recipe for the pork. I use a couple of different ones for ground pork from Hot Sour Salty Sweet. Or you can buy some flavorful meat and slice it. Whatever you want.
Drain the vegetables and put them on the bread with the protein and eat. Yum.