There are a couple ways to thicken the mixture. Bring the mixture to a vigorous simmer, uncovered, and let some of the liquid boil off. A quick and easy way to thicken sloppy Joes (and taco meat, too) is to add a tablespoon of masa to the mixture. Stir it in well and the mixture will immediately thicken. Add more, a teaspoon at a time, if it's still too "sloppy."