Cut baguette into ½-inch (1 cm) thick slices; arrange on baking sheet. Brush with 2 tbsp (25 mL) of the oil. Broil, turning once, until golden and crisp, about 2 minutes. Set aside.
In saucepan of boiling salted water, cook peas just until tender, 2 to 3 minutes. Drain and chill in ice water; drain well.
In food processor, puree together ricotta, remaining oil, grated Parmesan, mint, lemon juice, garlic (if using), salt and pepper. Pulse in peas until crushed but still chunky.
Top each crostini with some of the pea mixture. Garnish with Parmesan shavings.
