HEAT the oil in a large saucepan over a medium heat and cook the onion for 5 minutes, stirring occasionally. ADD the curry paste and garlic and cook, stirring, for a minute. ADD the coconut milk, stock, fish sauce, sugar and salt, then bring to the boil. ADD the red pepper and zucchini, cover with a lid, then reduce the heat to medium and simmer for 12 minutes. WHILE the curry simmers, cook the rice. ADD the chicken to the curry and simmer, covered, for a further 8 minutes. ADD the cornstarch paste and stir continuously until the curry thickens, then stir in the lemon juice and basil. SERVE on a bed of rice.