Prepare the base by heating olive oil in a large pot over medium heat. Add onions and sauté for 3-4 minutes until they become translucent.
Add the aromatics – garlic, carrots, and celery – and cook for another 5 minutes, stirring occasionally until vegetables begin to soften.
Introduce the spices by stirring in smoked paprika, cumin, and red pepper flakes (if using). Cook for 1 minute until fragrant – this crucial step blooms the spices and develops their full flavor.
Add the cauliflower florets and stir to coat with the spice mixture. Allow to cook for 3-4 minutes, stirring occasionally until cauliflower begins to take on some color.
Pour in the diced tomatoes with their juice, vegetable broth, rinsed lentils, and bay leaves. Stir well to combine all ingredients.
Bring the mixture to a boil, then reduce heat to maintain a gentle simmer. Cover partially with a lid and cook for about 25-30 minutes, or until lentils are tender and cauliflower is cooked through.
Finish the stew by removing bay leaves, adding lemon juice, and seasoning with salt and pepper to taste. The lemon juice brightens all the flavors and balances the smokiness.
Serve hot, garnished with fresh chopped parsley. For a complete meal, pair with crusty bread, a simple green salad, or a dollop of plain yogurt on top.