To make the mayo, combine the eggs, mustard, lemon juice, and a pinch of salt in a large jar – or the carafe of your Ninja Kitchen Foodi Power Mixer if you’re smart. Add the immersion blender to the mixture and pulse to combine. With the immersion blender on low, stream in the oil until the mayo is thick and creamy. Season with more salt and black pepper as desired.
Season the flat iron steak on all sides with Salt Pepper + Three Chiles blend set aside.
Thickly slice the tomatoes and season on both sides with salt. Wash and dry the lettuce.
Heat a large skillet or griddle over medium high heat. Fry up the beef bacon until crisp, about 4 minutes per side. Set aside to drain on paper towels. Melt the butter on the still hot skillet and toast the bread on both sides until golden. Finally cook the flat-iron steak over high heat for 3 to 4 minutes per side. Move to a cutting board and loosely tent with foil before slicing.
Slice the flat iron across the grain into thin strips. Build the sandwiches by swiping each piece of bread with mayo and then stacking the sandwiches with slice steak, bacon, tomatoes, and lettuce. Top with another bread side and cut in half to make it easier to fit into your mouth.