Preheat oven to 325 degrees.
Sauté onions in a skillet misted with oil spray for 8-10 minutes until soft and translucent.
Turn off heat.
Add the navy beans, BBQ sauce and balsamic vinegar to the onions.
Stir until well combined.
Transfer mixture to an oven safe baking dish and bake uncovered for 60 minutes until sauce is thick.
Serve hot!Nutrition per serving: 135 calories, 0.5 grams total fat.