Preheat the oven to 200°C fan. Spray 2 baking trays with some low calorie cooking spray.
Mix together the cornflour, chilli powder and garlic granules, with some salt and pepper.
Coat the vegetables with cornflour and then dip them into the egg whites. Finally, coat thoroughly with the panko.
Place the coated vegetables on the baking tray and spray with some low calorie cooking spray.
Bake in the oven for 15-20 minutes, turning the veg over halfway through, until golden brown and the vegetables are just cooked.
Mix the mayonnaise, sriracha, lemon juice and coriander together in a bowl and season to taste with some salt and pepper.
Serve the vegetable tempura immediately, alongside the dip.