Line a baking sheet with parchment paper, and preheat oven to 180 degrees Celsius or 375 degrees Fahrenheit.
Slice baguette into rounds horizontally, about ¼-1/3 inch thick, and place on parchment paper.
Combine olive oil and ¼ teaspoon of kosher salt in a small bowl.
Use a pastry brush to brush the olive oil and salt mixture onto the top of each baguette slice.
Toast in the oven for 10 minutes, until lightly browned.
Meanwhile, cut off radish greens (save them, and use for a salad or to make pesto), and rinse radishes.
Cut off tops and ends, then slice radishes thinly.
Combine ricotta cheese, lemon zest, lemon juice, and ¼ teaspoon of kosher salt in a small bowl.
After crostini have cooled for a few minutes, top with a small dollop of the ricotta cheese mixture and then with a few slices of radish.
Sprinkle generously with pepper, and top with a few sprinkles of chopped parsley, if desired.
Notes
Extra crostini toasts can be stored in a ziplock bag or airtight container for 1-2 days. Best reheated in oven or toaster. Leftover lemon ricotta spread will keep in the refrigerator for 3 days. If you don't have ricotta cheese, you can try this recipe with a mild goat cheese instead. You may want to reduce the amount of lemon juice if your goat cheese is quite tangy. Crostini can be baked, radishes prepped and sliced, and lemon ricotta spread made a few hours before serving. Wait to assemble until ready to serve though, since toasts will get soggy if made in advance.