Place the asparagus in a steamer set over 3 cups (750ml) boiling water and steam just until the asparagus is tender, 3 to 5 minutes. Remove from the steamer and let cool, then cut the stalks in half, lengthwise.
Prepare a bowl of ice water.
Bring a medium-sized saucepan filled with boiling, salted water (about 1 tablespoon of salt to 1-1/2 quarts/liters water). Add the peas to the boiling water, and when it returns to the boil, boil for 2 minutes then transfer the peas to the ice water to cool.
Drain the peas and place all but ½ cup in the work bowl of a food processor. Puree the peas and the mint leaves together, then add enough of the yogurt to make a lovely puree that is moist but of spreadable consistency. It will not be totally smooth, which is ideal! Adjust the seasoning to your taste.
Divide the pea and yogurt puree among the toasts. Top each with two half stalks of asparagus (trimmed to fit), and several peas. Shower the toasts with fleur de sel, and serve!