• In a large bowl, mix the eggs, parmesan cheese (if using), a pinch of salt, and black pepper. Whisk the egg mixture well.
• Add the baby spinach to a pan over medium heat, and let them wilt for a few minutes. Remove them from the pan and add them to the egg mixture.

Stovetop Option

• Heat the olive oil in a large non-stick pan over medium heat. Add the egg mixture and distribute it evenly across the pan. Cover the pan with a lid and check often. Once the outside edge of the frittata is slightly golden, flip the frittata and cook on the other side for a couple of minutes (note 1).

Oven Option

• Preheat the oven to 400F (200C). Heat the olive oil in an ovenproof skillet. Add the egg mixture and distribute it evenly across the pan. Cook for 5 to 8 minutes, then move the skillet into the oven and bake for 15 to 20 minutes or until the eggs are set.
• Peel the avocado, remove the seed, and mash it with a fork. Add the lemon juice, a pinch of salt, and black pepper.
• Toast the bread in a toaster or on the grill.
• Assemble the sandwich: Spread the avocado on the top half of the ciabatta bread. Add some lettuce leaves on the bottom layer, add a couple of slices of frittata, and four sundried tomatoes, then top each sandwich with the slice covered in mashed avocado.