Combine the lime juice, chilli, salt and sugar. Add the scallops and onion, mix, cover and leave to infuse in the fridge for approx. 2 hrs., mixing from time to time. Drain the ceviche, retain and set aside 2 tbsp of the lime juice.
Cut the avocado in half, remove the stone, scoop out the flesh, mash with a fork. Mix in the garlic, crème fraîche and 1 tbsp of the reserved lime juice, season with salt.
Mix the cucumber, peach, radish and coriander with the remainder of the lime juice and oil, season. Prepare the tortillas according to the packet instructions. Spread the avocado cream over the tortillas, top with the peach salad and ceviche.