Based on this recipe and this recipe.

cost: £5 skill: easy serves: 4
you can overcook lamb, but you can’t over-roast it.  Put this in the oven or slowcooker for at least 4 hours to achieve falling-off-the-bone tenderness.

1-2 pound cheap lamb cuts or shoulder joint (you want it well-marbled)
2 cloves garlic, finely minced
1 T sea salt
2 T ground cumin
1 pinch paprika
1 t thyme
1 T olive oil
1 large yellow onion, sliced
2 medium bell peppers, seeded and sliced
2 large chili peppers, thinly sliced

Set the oven at 160C/gas mark 3. Combine garlic with the salt using a pestle and mortar. Mix in the cumin, paprika and thyme. Gradually add the oil so that you end up with a thickish paste.

Put the lamb into a baking dish and rub it all over with the garlic mixture, add about 1 C water, then put in the oven for 35 minutes. Baste the lamb with the liquid, then continue roasting for a further three hours, basting and turning the meat every half hour or so. If the juices are evaporating add a little more water.

Add sliced chili and bell peppers and sliced onion to the casserole and stir until coated with cooking juices.  Crack over with some black pepper.  Return to the oven for another hour until the onions and peppers are tender.  Serve over rice with a good spoon of the cooking juices