For the dressing
Bring a large heavy pan of water to the boil, and stir in the rice. Return to the boil and cook for 12–15 minutes until tender. Drain and cool.
Cook the peas in a small pan of boiling water for about 2 minutes. Rinse under cold water. Drain well.
To make the dressing, whisk together the oil, juice, garlic and sugar in a small jug, then season with salt and pepper.
Combine the rice, peas, spring onions, peppers, sweetcorn and mint in a large bowl.
Pour over the dressing and mix well. Cover the salad with cling film, and refrigerate for 1 hour before serving.