Place quail eggs in a medium pot, and cover with a few inches cold water. Cover, and heat to the point of boiling over high intensity. Switch off intensity, and let sit 2 minutes, mixing a few times to guarantee in any event, cooking. Move eggs to a bowl of ice water, and let cool totally, around 5 minutes. Eliminate eggs, 1 all at once, and wipe off with paper towels. Strip eggs, and divide longwise. Eliminate yolks, and hold whites.
Crush yolks with mayonnaise, and season with salt and pepper. Mix in lemon juice.
Fill each egg-white half with 1/4 teaspoon caviar. Place a spot of egg-yolk combination on each crostini, and put an egg half on top. Serve right away.