Place lentils and vegetable broth in a medium saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 20 minutes or until lentils are tender. Drain any excess liquid.

Heat olive oil in a large skillet over medium heat. Add the onion and bell pepper, sautéing for 5-7 minutes until the vegetables are softened and translucent.

Add the minced garlic to the skillet and cook for 1 minute until fragrant.

Stir in the cooked lentils, tomato sauce, tomato paste, mustard, maple syrup, apple cider vinegar, smoked paprika, and chili powder.

Simmer the mixture over medium-low heat for 10 minutes, stirring occasionally, until the sauce has thickened and the flavors are fully integrated.

Adjust seasoning with salt and pepper to taste.

Spoon the lentil mixture onto the toasted hamburger buns and serve immediately.