Place the eggs in a large pot and cover them with water. Bring the water to a boil, then turn off the heat and let the eggs sit covered for 12 minutes.
Drain the hot water and run the eggs under cold water until they are cool enough to handle. Peel the shells and slice each egg in half lengthwise.
Remove the yolks and place them in a blender or food processor with the spinach, mayonnaise, mustard, salt, and black pepper. Blend until the mixture turns smooth and green.
Spoon or pipe the green filling back into the egg white halves.
Add two olive slices to each egg half to form eyes and cut a small strip of red bell pepper to create a mouth on each one.