Place lentils in a large pot, and cover with beer (enough so that there's at least a full inch or two of water above the lentils). Bring to a boil and reduce to a simmer.
Cook for 15 to 20 minutes, or until the lentils are chewable, but still have some firmness to them. Drain them and set aside.
Heat olive oil in a large pot over medium heat.
Add the onion and pepper, and cook for 5 to 8 minutes, or until the onion is soft and clear, stirring frequently.
Add the garlic, chili, paprika, and mustard, and continue cooking for another minute or two, until the garlic is quite fragrant.
Add the lentils, fire-roasted tomatoes, tomato paste, brown sugar or maple syrup, apple cider vinegar, salt, and pepper.
Bring the mix to a simmer, adding more broth as needed. Simmer until the mixture has thickened to your liking, about 15 to 20 minutes
Remove mixture from heat and allow to cool for a few minutes.
Divide sloppy joes onto the buns and top with toppings of choice, including some Tabasco or sriracha for heat, if desired. Serve