Heat 1 tablespoon oil in a frying pan, add the spinach leaves and cook for 1 minute until starting to wilt. Add the spring onion and garlic and cook for 1 minute more until wilted. Pour away any excess water, then stir in the crème fraîche.
Meanwhile, grill the bacon for 5–8 minutes until crisp, then cut into small pieces. Open the oysters, discarding the top shell, and arrange them on a baking sheet. Spoon over some of the spinach mixture (together with any oyster juices) and add some bacon pieces. Mix the breadcrumbs with the cayenne and sprinkle over the top.
Drizzle over the remaining oil and bake in a preheated oven, 230°C (450°F), Gas Mark 8, for 10 minutes or until the breadcrumbs are crisp.