This is another ridiculously easy one pot meal. If you are sans slow cooker then make it up and cook slowly for 45 mins or so instead.
For 4-6 people you need:
1 onion, chopped
1 tbsp olive oil
1/2 cup quinoa
1/2 cup pearl barley
1-1.5 litres stock (use a little more if cooking on the stove)
1 celeriac, diced into 1cm cubes
3-4 carrots, peeled and thickly sliced
Fry off the onions in the oil for 5 mins or so. Add everything else to the slow cooker and cook on low for 6-8 hours. Serve with mash.