In a small saucepan off of heat, whisk together soy sauce, brown sugar, cornstarch garlic, and ginger to blend, along with ¼ cup cold water.
Place the saucepan over medium-high heat and bring it to a strong simmer, then reduce to low. Simmer 3 minutes more. Sauce will thicken to a thick glaze.
Heat oil in a skillet over medium-high. Add desired protein to the pan and cook until browned and fully cooked through, 4–7 minutes per side depending on cut and thickness.
Add prepared teriyaki sauce and stir until coated and glossy, about a minute.
