Preheat the oven to 200°C (400°F), Gas Mark 6. Use a rolling pin to roll the bread out thinly. Cut each slice into a circle, approximately 12 cm (5 inches) in diameter, and press the circles into 4 large nonstick muffin or Yorkshire pudding tins. Cook in the preheated oven for 7–8 minutes, until crisp and golden.
Meanwhile, mix the crumbled feta with the spring onions, walnut pieces and tomatoes. Season to taste, then spoon the mixture into the toasted tart cases. Drizzle with the olive oil and serve with a mixed leaf and cucumber salad.