Brown the beef. Heat 1 tablespoon oil in a large Dutch oven over medium-high heat. Add the ground beef in a fairly even layer and let it cook undisturbed for 2–3 minutes so it develops a good brown crust. Break it apart and continue cooking until deeply browned, about 5–7 minutes total. Transfer to a plate, leaving about 1–2 tablespoons of fat in the pot.
Build the flavor base. Reduce the heat to medium. Add the remaining oil if needed, then add the onion, bell pepper and jalapeño. Cook for 5–6 minutes until softened and beginning to caramelize. Add the garlic and cook for 30 seconds.
Caramelize the tomato paste. Add the tomato paste and cook, stirring frequently, for about 2 minutes, until it turns darker brick red. Don't skip this—it makes a noticeable difference.
Bloom the spices. Add the chili powder, cumin, smoked paprika, oregano, coriander, cayenne and cocoa powder. Cook for about 30 seconds, stirring constantly, until fragrant.
Simmer. Return the beef to the pot. Add the fire-roasted tomatoes, beef broth, lentils, Worcestershire sauce, brown sugar, bay leaf, salt and pepper. Stir well and bring to a gentle boil.
Reduce the heat to low, partially cover, and simmer for 35–45 minutes, stirring occasionally, until the lentils are tender and the chili is thick. Add a splash of broth if it becomes too thick before the lentils are cooked.
Finish it. Remove the bay leaf. Stir in the lime juice. Taste and adjust the salt, pepper and chili powder if necessary. Simmer uncovered for another 5 minutes if you'd like it thicker.
Remove from the heat and let the chili rest for 10 minutes before serving. Stir in the cilantro or parsley.