Place the tomato paste, broth, sweetener, vinegar, lime juice, fish sauce, salt, garlic powder and ginger in a medium-zied saucepan over medium heat. Stir well to combine. Bring the mixture to a boil, stirring often. Boil for 3 minutes, stirring occasionally, until thickened to your liking. Remove from the heat and let cool. Sift in the guar gum, if using, and whisk until well combined. Pour the sauce into a jar and refrigerate until ready to use.