This steak may be cubed, but it sure ain't square.
First, the marinade. Combine bosc pears, soy sauce, sesame oil, brown sugar, ginger, garlic, and 2 of the sliced scallions in a food processor. Pulse the whole thing until it's finely chopped, should take about 15 times. Reserve 1/4 cup of the marinade mixture in a small bowl.
Combine the steak, the 3/4 marinade mixture, and 1/4 teaspoon of the crushed red pepper in a medium bowl. Cover and let it chill for 2 hours.
Heat 1 tablespoon of the oil in a large cast-iron skillet over high. Using tongs, transfer half of the steak from marinade to hot oil in skillet. Cook it while frequently stirring until the steak is cooked through and edges are crisp. Transfer to a serving platter.
Repeat step 3 with the remaining 1 tablespoon oil and remaining steak. Drizzle the reserved marinade mixture over the steak, then sprinkle with salt, sesame seeds, and remaining 2 sliced scallions and 1/4 teaspoon red pepper. Serve with rice, cucumbers, kimchi, and butter lettuce leaves.