Lay out the crostini on a sheet tray and toast under the broiler quickly. Once toasted, rub the bread with the garlic clove.
Add the pea shoots to a mixing bowl with the olive oil and a generous amount of salt. Squeeze the juice from the lemon half over the pea shoots and mix well with a wooden spoon. Spread the pea shoot mixture over the crostini and fan the radishes over the top.
Adding some anchovies--either salted or otherwise preserved--over the top of these makes the dish pretty much a meal.