Cut the beef and tofu into bite-sized pieces.
Sprinkle salt on the tofu and let it sit for 5 minutes.
Heat cooking oil in a pan and grill the tofu on both sides until golden brown.
Move the tofu to the side of the pan and add the beef to stir-fry.
Add soy sauce, minced garlic, sugar, water, and pepper. Stir-fry together over high heat.
Add green onions and simmer over medium heat until the sauce thickens.