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 garlic and cook for 1 minute until fragrant.
03 - Add ground beef. Cook, breaking it up with a 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 lentils, diced tomatoes with 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 for desired consistency.
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.