Heat the oil in a frying pan, and in it fry the tortillas, one at a time, until crisp. This will take about 2 minutes each. When cool, spread each with the creme fraiche.
Gently mix, in the order given, the onions, tomato, coriander, jalapeño, lime, shrimps and seasoning. Cover each tostada with the shredded lettuce, heap the shrimp mixture on top, and spoon the diced avocado over it, finishing off with any remaining creme fraiche.
© 2000 Frances Bissell. All rights reserved.