Heat 2 Tbsp. oil in a large skillet over medium. Add onions, season with salt, and cover. Cook, uncovering and stirring occasionally, until onions are softened and just beginning to take on color, about 5 minutes. Uncover, add ginger, and cook, stirring occasionally, until onions are jammy and golden brown, 10–12 minutes. Stir in soy sauce. Transfer onion mixture to a plate and wipe out skillet.