Heat 2 tablespoons oil in a medium saucepan over medium low heat and add the shallots and garlic. Cook until shallots are softened, 3-4 minutes then add the peas and broth. Raise the heat to bring the liquid to a boil, then reduce to a simmer and cover the pan. Cook until the peas are tender, 8-10 minutes for fresh peas and 4-5 minutes for frozen.
Transfer the contents of the pan to a food processor and add the lemon zest, mint and grated Parmigiano-Reggiano cheese. Puree until smooth. Add the ricotta and pulse until just combined. Season the mixture with salt and pepper to taste.
Arrange the baguette slices on a baking sheet and brush them on both sides with the remaining olive oil. Place the sheet under the broiler and cook 1-2 minutes until lightly toasted. Flip the bread over and lightly toast on the other side.
Spread some of the pea and ricotta mixture on each slice of baguette. Top each one with some Parmigiano-Reggiano shavings and mint.