Step 1 Preheat oven to 200°C. Cut roots and 3cm of stalks from coriander. Wash well and chop finely. Reserve remaining coriander. Spray a 20cm cake tin with oil and line with baking paper.
Step 2 Spray a large non-stick frying pan with oil. Cook onion over a medium heat, stirring, for 3 minutes, or until soft. Add coriander root and stalks and Mexican seasoning. Mix well.
Step 3 Add chicken to onion and cook, stirring often, for 5 minutes, or until browned. Stir in tomatoes and bring to the boil. Reduce heat and simmer for 4-5 minutes, or until mixture becomes a thick sauce. Stir through 1/4 cup roughly chopped coriander leaves. Cool.
Step 4 Place one tortilla in the base of cake tin Top with a third of the sauce. Sprinkle over a third of the spinach and a third of the cheeses. Continue layers, ending with a tortilla. Spray with oil. Bake for 15-20 minutes, or until top is light golden brown. Stand for 10 minutes before transferring to a serving platter. Top with avocado and coriander leaves.