Mix the garlic, zest and juice of 1 lime, the chilli and 1 tbsp oil together in a bowl, then season. Add the prawns, coat well and leave to marinate for an hour.
Put the avocado, coriander, parmesan, pine nuts, 3 tbsp oil and the remaining lime zest and juice in a blender and blitz until just smooth. Season.
Set a griddle pan over a high heat, add the bread and cook for 1-2 minutes on each side until lightly charred. Set aside.
Heat the remaining oil in the same pan set over a medium-high heat. Add the prawns and cook for 1-2 minutes on each side, until just cooked through and lightly charred.
To serve, spread the avocado pesto over the toasted bread and top with the prawns.