Heat two tablespoons of the oil in a pan and gently fry the leek and garlic for 2-3 minutes, or until softened. Add the tuna and thyme, stir well and pour in the cream. Simmer for 4-5 minutes.
Heat a chargrill pan, drizzle the bread with the remaining oil and griddle the bread for 2-3 minutes on each side, or until golden-brown and crisp.
Serve the leek and tuna mixture on top of the toasted bread, garnished with the fresh herbs.