1) Place radishes, carrot and onion in a medium bowl. Cover with cold water and let soak for 5 minutes. Drain.
2) Combine soy sauce, lemon juice, scallions and ginger in a small bowl. Add 2 tablespoons of the mixture to the drained vegetables and toss. Set aside the remaining sauce.
3) Season steak on both sides with salt and pepper. Heat oil in a large nonstick skillet over medium-high heat. Cook the steak 3-4 minutes per side for medium rare. Let rest on a cutting board for 5 minutes, then thinly slice and serve with the vegetables, drizzled with the reserved sauce.