Peel and dice the onion and the sweet potato. Place a medium pan on a medium-heat and add ½ tbsp oil, the onion and the sweet potato. Season with a pinch of salt. Fry for 5 mins, stirring often, till the veg have started to soften and caramelise.
While the veg fry, peel and crush or grate the garlic. Drain the beans and rinse them under cold running water.
Stir the garlic into the frying veg with 1 tsp each dried oregano and Cajun spice mix. Cook and stir for 1 min.
Tip in the beans and stir them into the veg. Pour in the passata. Stir to mix, then pop on a lid and simmer the sauce for 25 mins till the veg are tender. Sir every so often and add a splash of water if the sauce thickens too quickly.
While the veg simmer, heat your grill to high. Crumble half the pack of feta (see our tip for what to do with the leftovers).
Lay 1 tortilla wrap in the base of a 20cm-round, loose-bottomed cake tin. No cake tin? Just use an ovenproof dish that you can snugly fit the tortilla into the base of.
Taste the sauce and add a pinch more salt or Cajun spice mix if you think it needs it. Spoon a third of the sweet potato and black bean chilli over the tortilla. Cover with a second tortilla, and repeat till you’ve used all the chilli and all the tortillas – you’ll finish with a tortilla on top.
Scatter the feta over the tortilla and slide under the grill. Cook for 10 mins till the feta is golden and melted. While the tortilla stack cooks, pick the coriander leaves off their sprigs.
Serve the tortilla stack in slices, garnished with the coriander leaves and with handfuls of the salad mix on the side.