For the quick-pickled vegetables: Bring the rice vinegar, sugar, chile paste and 1/2 cup water to a boil in a small saucepan. Combine the radishes and carrots in a small bowl and pour the pickling liquid over the top. Set aside and allow to cool and pickle while you prepare the remaining ingredients, at least 20 minutes or up to 1 hour.
For the rib-eye steak: Heat the olive oil in a large heavy-bottomed skillet over medium to medium-high heat. Sprinkle the steak on all sides with the salt and pepper. Place the steak in the skillet and cook until it reaches the desired temperature, about 4 minutes per side for a perfect medium-rare. Meanwhile, mix the butter and soy sauce together in a small bowl. Remove the steak to a plate and immediately spread the soy butter over the top. Let the steak rest and the butter melt into the steak, 5 to 7 minutes.
For the spicy mayonnaise: Mix together the mayonnaise, chile paste and sesame oil in a small bowl until completely combined. Set aside.
To assemble: Using a sharp knife, split the baguette through the middle. Spread the top and bottom with the spicy mayonnaise. Thinly slice the steak and shingle it on the bottom of the bread. Drain the pickled carrots and radishes and place on top of the steak. Finish with the cucumber ribbons and cilantro. Cut the sandwich into thirds or fourths and serve.