Preheat the oven to 200℃ (180℃ fan)/400°F/gas mark 6. Place the onion and pepper in a roasting tin and drizzle with 1 tablespoon of the olive oil. Toss the vegetables together so that they are coated in the oil and spread out into an even layer. Roast for 15 to 20 minutes until just soft and just beginning to char. Remove from the oven and allow to cool.
Meanwhile, cook the rice. Rinse the rice until the water runs clear. Place in a saucepan with plenty of lightly salted water. Bring to the boil, reduce heat, stir and simmer for 8 to 10 minutes or until rice is tender.
Once the rice is cooked remove from the heat and drain, then rinse in cold water and drain again.
Place the rice, roasted peppers and onions in a serving bowl and toss to combine. Whisk together the remaining oil, vinegar, mustard and seasoning with a fork and pour over the rice. Toss again to coat the rice in the dressing.
Sprinkle the mixed seeds over the rice and serve.
Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)