It's a little outside my field, but I can give you the basics.

As you know, the stomach mashes up the food to be digested and physically churns it, but it also releases enzymes to help break the food down into even smaller parts so it can be absorbed into the body through the walls of the intestines. Enzyme chemistry isn't necessary to know, I guess very basically you can think of them as little proteins with a specific shape that attach to specific food molecules and split them in two. An enzyme responsible for breaking down proteins is secreted by the stomach, called Pepsin. Pepsin secretion is stimulated by physical stimulation of the walls of the muscles, so the more food in the stomach, the more pepsin is released and it also stimulates the muscles in the stomach wall to churn, actually how this works is too complicated to explain in simple terms.

Ginger contains a mild irritant, which is partly responsible for the earthy/tangy flavour. This irritant is produced by the ginger plant probably to ward off small underground bugs, but for humans the irritation is mild so we think of it as a flavour thing. Now, this irritant is mostly made of a protein that you don't need to know the name of, and it is acts in a way to stimulate the stomach to produce more pepsin and churn faster (long story, the essentially the mild irritation is confused for pressure on the wall of the stomach so it thinks there is more food than there is). This means you can digest the food and especially protein faster and so the food is digested faster and more fully.