Heat the slow cooker to medium.
Place the lamb cubes into the bottom of the slow cooker.
Add the onion, garlic, tinned tomatoes, stock cubes, oregano, thyme, fennel, cumin, salt and pepper, and stir well.
Place the lid on and cook for 3.5-4.5 hours on HIGH (or 6-8 hours on LOW).
When the lamb is just tender, tip in the dried orzo (see notes), peppers and water stir through. Cook for a further 45 minutes.
When the orzo is just cooked, squeeze over the lemon juice, sprinkle over the feta and mint and serve.