Step 1 Preheat oven to 160°C. Line a large baking tray with non-stick baking paper. Place quinoa into a small saucepan with 1 1/2 cups water and bring to the boil. Reduce heat to low, cover and simmer for 12 minutes, or until water is absorbed. Remove from heat, set aside to cool.
Step 2 Meanwhile, cut tops off each tomato. Scoop out flesh and pulp, and reserve, leaving a 1cm-thick shell. Roughly chop reserved tomato flesh. Halve each eggplant lengthwise, scoop out flesh, leaving a 1cm-shell, finely chop flesh and reserve.
Step 3 Place a large non-stick frying pan over medium heat and spray with oil. Add onion, cook stirring occasionally, for 3–4 minutes or until soft. Add reserved eggplant, garlic, paprika and chilli flakes, cook for 2 minutes more. Place onion mixture into a large bowl with reserved tomato pulp, cooked quinoa, mince, feta and coriander. Stir until all ingredients are well combined and season with black pepper.
Step 4 Stuff tomatoes, capsicums and eggplant shells with the quinoa mixture. Place eggplants and capsicums onto prepared tray. Bake in preheated oven for 10 minutes. Add tomatoes to tray and return to oven for a further 20–25 minutes, or until vegies are tender, stuffing is golden and mince is cooked through.