In a large mixing bowl, whisk eggs, milk, salt, pepper.
Add onions, tomatoes, chopped spinach leaves in a baking quiche mould. Pour the egg mixture from the top.
Garnish with tomato slices and grated parmesan cheese.
Add water into an instant pot and place the rack.
Place the quiche mould on the rack.
Set to the “Manual” at high pressure for 10 minutes.
Select “Cancel” and release pressure quickly.
Remove the quiche from the Instant Pot and serve hot.