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 it.
03 - Add ground beef to the pot. Cook, breaking it up with a wooden spoon, until browned and no longer pink.
04 - Stir in tomato paste, oregano, 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 well, scraping up any browned bits from the bottom of the pot.
06 - Bring 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 more broth or water if needed.
07 - Season with salt and pepper to taste. Remove bay leaf before serving. Serve hot over whole wheat pasta, zucchini noodles, or rice. Garnish with fresh herbs and Parmesan if desired.