Rinse lentils and add to a saucepan. Add the water and bring to a boil. Once boiling, lower to a simmer, cover, and cook about 10 minutes. Taste and make sure they are cooked through. Drain and set aside.
Heat olive oil in a sauté pan over medium. Add the onion and bell pepper and cook for 5-8 minutes, until softened. Add the garlic and cook another 30 seconds to 1 minute, just until fragrant.
Pour in the drained lentils along with the chile powder, paprika, oregano, salt, tomato sauce, and tomato paste. Cook for 10 minutes to meld flavors, stirring occasionally. If mixture looks too dry, add ½ to 1 cup water. It should be saucy but not runny.
Stir in the maple syrup (if using) and mustard and heat through. Serve on toasted hamburger buns or wrap of choice.
Notes
If using green or brown lentils, increase cooking time to 20-25 minutes.