Cook the quinoa according to the packet instructions, then drain and keep warm.
Meanwhile, chop the onion and garlic. Thinly slice the red pepper and cavolo nero.
Heat a spoonful of olive oil in a pan and gently sauté the onion for 5 minutes. Add the garlic, chilli flakes and herbs, then cook for another minute. Add the tomatoes and red pepper slices, then (under a lid) cook for 5-8 minutes until the veggies have softened (but are not mushy) over medium heat.
Add the cavolo nero slices and a splash of water or fresh lemon juice and steam under cover for 3-5 minutes.
Stir in the olives and the drained quinoa. Season with salt & pepper and combine well.
Serve with basil leaves and crumbled feta (vegan, if preferred) scattered over the dish.