01 - Heat olive oil in a large pot over medium heat. Add onion, carrots, celery, and red bell pepper. Sauté for 6–8 minutes until softened.
02 - Add minced garlic and cook for 1 minute until fragrant, being careful not to burn.
03 - Add lean ground beef to the pot. Cook, breaking it up with a wooden spoon, until browned and no longer pink throughout.
04 - Stir in tomato paste, dried oregano, dried basil, bay leaf, and red pepper flakes. Cook for 2 minutes to develop flavors.
05 - Add rinsed lentils, diced tomatoes with their juice, and broth. Stir thoroughly, scraping up any browned bits from the bottom of the pot.
06 - Bring mixture to a boil, then reduce heat to low. Cover and simmer for 35–40 minutes, stirring occasionally, until lentils are tender and sauce has thickened. Add additional broth or water if consistency becomes too thick.
07 - Season with salt and pepper to taste. Remove and discard bay leaf. Serve hot over whole wheat pasta, zucchini noodles, or rice. Garnish with fresh herbs and Parmesan cheese if desired.