I visited this truck at the Southpark Eats Alternative Wednesday food truck fest (off Fairview at Piedmont Row Dr. South - tons of nearby parking!).
Lemongrass beef Banh Mi was DELICIOUS - great flavor in beef and sauce - a little kick but not too spicy. Baguette was outside crisp and inside chewy - as it should be. Mine was sans pickled daikon (allergic) and jalapeƱos (don't like) but had plenty of cucumber and cilantro.
My coworker got the lemongrass chicken bowl with a bonus cracked egg & it looked wonderful. She said it was tasty and not spicy.
Note: we got to trucks relatively early yet I got the last order of lemongrass beef.
Definitely give Yummi Banh Mi a try.