In a saucepan, bring the water and lentils to a boil.
Reduce the heat and simmer 20 minutes or until the lentils are tender.
Meanwhile in a large skillet, cook the onion, garlic, celery, and bell pepper until the onion is soft
Add a bit of water to the skillet if it sticks.
Add tomato sauce, maple syrup, worcestershire sauce, balsamic vinegar and paprika to the skillet.
Simmer over low heat until the lentils are cooked.
Drain any extra water from the lentils and combine them with the sauce.
Serve on buns, topped with red onion if desired.