In a saucepan, combine the soaked Puy lentils with 710ml (1¼pt) of water and a pinch of salt.
Bring it to a boil, then reduce the heat to medium-low.
Cover with a lid and cook for 18-20 minutes.
Drain the lentils in a colander.
In a frying pan, heat a thin layer of olive oil over medium heat.
Add the diced red onion and yellow bell pepper, season with salt, and sauté for 4-6 minutes, covered, until the onion turns translucent.
Stir in the tomato purée and cook for 1 minute.
Add the sweet smoked paprika, ground cumin, and ground coriander along with the chopped garlic, and cook for 30 seconds.
Stir in the canned chopped tomatoes and saffron (if using).
Cover and let it simmer over medium-low heat for 15 minutes.
Add the cooked lentils and cook for an additional 10 minutes, allowing the liquid to reduce slightly.
Stir in the chopped spinach and let it wilt.
Remove the stew from the heat and stir in the harissa and honey.