Heat oil in a small saucepan over medium heat; sauté shallots and jalapeño until very tender (about 7 min.). Add vinegar, sugar and tamari. Increase heat to medium-high heat; bring to a boil. Reduce heat to low and simmer, stirring occasionally, until reduced to about ¼ cup (about 10 min.). Remove sauce from heat and cool to room temperature before using. Sauce may be stored, covered, in the refrigerator for up to 3 days.