Unfold the pastry sheet, brush with butter, then cut into 32 small squares about 5 cm (2 inches) each. Gently press 1 square into 16 sections of 2 × 12-section mini muffin tins, then add a second square of pastry to each at right angles to the first for a petal-like effect.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 4–5 minutes until golden. Lift the filo cups out of the tins and cool on a wire rack.
Halve, stone and peel the avocado, then mash with the lime juice or blitz in a food processor. Add the chilli, spring onion and coriander, season lightly with salt and pepper and mix together.
Spoon the guacamole into the filo cups, garnish with extra chopped chilli and coriander, if liked, and serve within 1 hour of finishing as the avocado discolours.