Heat half the oil in a large flameproof casserole over a medium-high heat. Tip in enough beef to cover the base of the pan in a single layer, being careful not to overcrowd the pan. Brown the beef on each side, turning until it has a deep brown crust all over – this will give the stew a deep, beefy flavour. Remove to a plate using a slotted spoon and continue cooking until all the beef is browned. Set aside.
Heat the remaining oil in the same pan, then tip in the onions, reduce the heat to low-medium and sizzle for 8-10 mins until soft, stirring and scraping the base of the pan to lift any browned bits.
Add the garlic, cumin, coriander, paprika, cinnamon and tomato purée. Stir for 1-2 mins until the spices are sizzling and aromatic, then tip in the chopped tomatoes and chipotle paste, if using, and crumble in the stock cubes. Return the beef to the pan with any resting juices, pour in 1.2 litres water, season and bring to a simmer.
Once bubbling, reduce the heat to low, cover with a lid and simmer for 1 hr 45 mins, stirring occasionally. Meanwhile, tip the lentils into a bowl, cover with cold water and leave to soak. Drain, then add to the stew, cover again and continue to cook for 45 mins more, or until the beef and lentils are tender.
Tip in all the beans, return to a simmer and bubble for 5 mins until the beans are warmed through. If your stew is soupy and you prefer it thicker, boil, uncovered, for a few minutes more until reduced to your liking. Taste for seasoning and add more salt or chipotle paste, if you like; it may also need some sugar depending on the tomatoes you’ve used (add up to 2 tsp). Will keep chilled for two days or frozen for two months. Leave to cool completely first.
If making the tortilla croutons, cut the wraps into small triangles and heat enough oil to cover the base of a deep frying pan. Fry over a medium heat for 2-3 mins, tossing in the pan until crisp. Or, simply crumble tortilla chips to make a quick, crunchy topping.
Serve the stew in bowls topped with your choice of feta, soured cream or yogurt, coriander, avocado and sliced chilli, lime wedges on the side for squeezing over and the tortilla croutons. Grind over some black pepper, if you like, before serving.