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 and fragrant.
02 - Stir in minced garlic and cook for 1 minute until aromatic, being careful not to burn it.
03 - Add lean ground beef to the pot. Cook, breaking up meat with a wooden spoon, until fully 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 deepen flavors and toast the spices.
05 - Add rinsed lentils, canned diced tomatoes with their juice, and broth. Stir thoroughly, scraping up any browned bits from the pot bottom to incorporate flavor.
06 - Bring mixture to a boil, then reduce heat to low. Cover and simmer for 35–40 minutes, stirring occasionally. Cook until lentils are tender and sauce has thickened. Add additional broth or water if sauce becomes too thick.
07 - Remove bay leaf and discard. Season generously with salt and freshly ground black pepper to taste.
08 - Serve hot over whole wheat pasta, zucchini noodles, or rice. Garnish with fresh chopped herbs and grated Parmesan cheese if desired.