Mix the greek yogurt with the juice of half a lemon. Season with salt and pepper and set aside.
Wash and peel the avocado and pear, cut them into thin slices.
On each slice of bread, spread the yoghurt and lemon mixture, then place the avocado and pear strips on top, alternating them. Sprinkle with a few drops of lemon.
Sprinkle the toast with chia and sesame seeds, then add three slices of onion on top of each slice of bread.