Lay the bread slices on a baking sheet, brush lightly with 1 tablespoon of the oil and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 5–6 minutes until crisp and golden. Leave to cool on a wire rack while you prepare the pesto.
Cook the peas in a saucepan of lightly salted boiling water for 3 minutes. Drain and immediately refresh under cold water. Put the peas in a food processor, add the remaining oil, the garlic, ricotta, lemon juice, mint, Parmesan and salt and pepper and process until fairly smooth.
Spread the crostini with the pesto and serve drizzled with oil.