Heat oil in a 2-quart pan on medium heat. Add onion and cook 3 minutes or until softened.
Add garlic, chili powder and mustard powder; cook 1 minute or until fragrant (do not brown garlic).
Add broth, tomato sauce, balsamic vinegar, mustard, honey and lentils; stir well and bring to a boil.
Reduce heat to low; cover and simmer 30 minutes until lentils are tender, but intact. (Cooking times for lentils vary. If necessary, add 1/4 cup water and simmer 5 minutes longer.) Season with salt and pepper.