Add olive oil, onion, and garlic to the slow cooker.
Pour in crushed tomatoes, diced tomatoes, and tomato paste.
Stir in lentils, oregano, basil, thyme, smoked paprika, salt, and black pepper.
Add maple syrup for a touch of sweetness, if desired.
Pour in vegetable broth and mix everything well.
Cover and cook on low for 6 hours.
Stir, taste, and adjust seasoning before serving.
Serve over pasta or use as a pizza sauce.