Preheat the oven to 425 degrees F. Arrange baguette slices on a baking sheet and brush with a little bit of olive oil. Bake for 5 to 6 or until crisp and golden brown. Let cool.
Pulse the peas, mint, garlic, Parmesan, and lemon juice in a mini food processor until combined, but still chunky. With the machine running, add the olive oil in a steady stream until it reaches the desired consistency. Season with salt and pepper to taste.
To serve: spread about a tablespoon of ricotta on each crostini. Top with a teaspoon of pea pesto. Garnish with additional chopped fresh mint and a drizzle of olive oil if desired. Serve immediately.