Preheat oven to 180°C. Heat oil in a frying pan over medium-high heat. Reserve 2 tablespoons onion. Add garlic and remaining onion to pan. Cook, stirring, for 3 minutes or until soft. Add mince. Cook, breaking up mince with a wooden spoon, for 8 minutes or until browned. Add capsicum, corn and chilli powder. Cook, stirring, for 3 minutes or until capsicum is just tender. Stir in diced tomatoes. Reduce heat to medium. Simmer, stirring, for 5 minutes or until mixture is thick. Add half the coriander. Season with salt. Stir to combine. Set aside for 10 minutes to cool. Place a 6cm-deep, 20cm round springform pan on a baking tray. Place 1 tortilla in base of pan. Spread one-third of the mince mixture over tortilla. Sprinkle with 1/3 cup of cheese. Repeat layers twice with remaining tortillas, mince mixture and cheese, finishing with 1 tortilla. Sprinkle with remaining cheese. Bake for 15 minutes or until cheese is golden. Set aside for 5 minutes before removing from pan. Meanwhile, combine chopped tomato, reserved onion and coriander in a bowl. Serve pie with tomato mixture.