Combine the cucumber, olives, herbs, green pepper, radishes and spring onions (if used) with 3 tablespoons of the oil and the lemon juice. Season with pepper and set aside.
Heat a frying pan or griddle pan to medium-hot and toast the bread for 1–2 minutes on each side until golden and slightly charred. Toss the cheese in the remaining oil and lemon rind and season with pepper, add to the pan and cook for 3–4 minutes, turning once, until golden.
Put a cheese slice on top of each piece of toast and serve with the salad.