If using flank steak, follow same instructions.
If using tofu, line a plate with a paper towel. Cut tofu into 1" dice and place on towel-lined plate. Top with paper towels, then press gently but firmly to remove excess moisture, at least 5 minutes. Season with 1/4 tsp. salt and a pinch of pepper. Follow same instructions as steak strips in Step 3, stirring occasionally until lightly browned, 5-7 minutes.
If using shrimp, pat dry and season all over with a pinch of salt and pepper. Follow same instructions as steak strips in Step 3, cooking undisturbed until seared on one side, 2-3 minutes. Flip, and cook until shrimp reaches minimum internal temperature, 1-2 minutes.