Preheat oven to 180°C or 160°C fan forced. Grease an 2-litre with oil spray.
Place rice, zucchini, capsicum, corn and onion in a large bowl. Mix to combine. Spread into prepared dish.
Mix together eggs, buttermilk and sweet chilli sauce in a jug. Season well. Carefully pour over rice mixture, using a fork to move around mixture to allow egg to evenly combine. Scatter over feta. Bake for 40 minutes or until egg is set and golden.
Meanwhile, make chimichurri sauce. Place parsley, coriander, garlic and oil in a small blender. Blend until coarsely chopped. Stir through chilli flakes.
Cut frittata into squares. Serve with salad and chimichurri sauce.