Heat oven to 350°. Arrange baguette slices on a cookie sheet and toast in the oven until lightly browned, about 7 minutes.
In the bowl of a food processor, combine beans, walnuts, olive oil, onion, lemon juice, and rosemary leaves; puree until smooth. Season to taste with salt and pepper.
Spoon dip into a serving bowl and arrange toasted baguette slices on a platter around it. Garnish with rosemary and walnuts.