Step 1Combine coriander, cumin, chilli, lime juice, garlic and olive oil in a medium glass or ceramic dish. Add prawns and stir to coat. Cover and set aside to marinate in fridge for 30 minutes.
Step 2Meanwhile, preheat oven to 180°C. Line a baking tray with baking paper. Cut tortillas into 12 rounds using a cookie cutter; place on prepared tray and spray with oil. Bake for 6–7 minutes, turning halfway through cooking time, until golden and crisp. Set tortillas aside to cool.
Step 3Combine tomato, shallots, extra coriander and lime in bowl; stir to combine and season with pepper.
Step 4Set a large char-grill pan over high heat. Drain prawns of excess marinade and grill for 1–2 minutes each side, or until lightly charred and just cooked through.
Step 5Spread half a teaspoon of mashed avocado over each tortilla round. Top avocado with a grilled prawn and spoon tomato salsa on top. Serve immediately.