Plastic wrap the flat iron steak and stick it in the freezer to harden up (it shouldn't freeze) and make it easier to slice
Thinly slice the green onions and chili pepper, cut lime into wedges, and roughly chip the cilantro and basil
Prepare the broth by combining the pho concentrate with 4 cups of water and bringing the mixture to boil, then reducing to simmer
Remove the flat iron steak from the freezer and cut into thin slices, following the grain. Add steak slices to serving bowl.
Bring another pot of water to boil, add vermicelli and cook for 3 minutes (or until tender), then strain.
Add the noodles to the serving bowl with beef, top with bean sprouts, and pour the simmering hot broth on top of everything. The beef should cook within a few minutes, and will be done when it's no longer red.
Add the green onions, chili pepper, basil and cilantro as desired, and add lime.
The soup can then be flavored with as much or as little sriracha and hoisin sauce as desired.
Traditionally, the broth is made from beef bone marrow, but to save time we'll use a concentrate.The time it takes to cook the vermicelli depends on whether you're using thin or thick, but will generally by 3-5 minutes and can be done right at the end.