To blanch the spinach, fill a medium saucepan with water. Bring to a boil, add the spinach, and boil for 30 seconds. Meanwhile, fill a medium bowl with ice water. Remove the spinach from the pan and place in the ice water for 2 minutes, then drain well and blot dry with paper towels.
Place a crepe on a serving platter, spread with 30 g mayonnaise, and cover with the spinach. Top with another crepe, spread with another 30 g mayonnaise, and top with the tomatoes. Continue this process with 4 more crepes and the sweetcorn, smoked salmon, and green beans. Top with the remaining crepe and cover the top of the cake with the sliced avocado. Cut into wedges and serve.