Hard-boil eggs. Cool to room temperature and peel.

Drain tuna and scoop into a medium bowl. Add avocado, juice of lemon and diced onion to tuna. Season with salt and pepper and mash together. Chop eggs and fold into tuna mixture.

Toast bread. Layer 4 slices with tuna mixture and spinach. Top with remaining 4 slices of toast. Cut in half and serve with raspberries.