Combine first 4 ingredients in a small bowl, stirring with a whisk.
Heat oil in a large Dutch oven over medium heat. Add garlic, and cook for 1 minute, stirring frequently. Gradually add spinach; cook for 2 minutes or until spinach wilts, stirring constantly. Place spinach in a colander, pressing until barely moist. Place spinach in a medium bowl; drizzle with soy sauce mixture. Toss well to coat.
I was plesantly surprised at how good this was on the spinach because I tasted it straight and it was a little biting with the vinegar. Served with Praline Salmon (also on this site and delicious) and roasted potatoes. I will definitely make it again.