Whisk together gluten-free self-raising flour and white rice flour in a bowl. Gradually add ice-cold water and cold jumbo egg, mixing until mostly smooth. Cover and refrigerate for 10 minutes.

Rinse and slice red capsicum, eggplant, and zucchini into uniform pieces, about 5mm thick. Prepare optional vegetables if using.

Heat cooking oil in a large frying pan or deep skillet to about 170°C (350°F). Use a wooden spoon to test.

Dip vegetables into chilled batter, coat evenly, and carefully place them in hot oil. Fry for 2-3 minutes on each side until light golden.

Remove fried tempura vegetables with a slotted spoon and drain on paper towels. Repeat until all are cooked; serve hot with dipping sauces.