Bring a large pot of salted water to a rolling boil. Reduce the heat to a heavy simmer, and carefully add the eggs. Boil the eggs for 9-15 minutes depending on altitude (9 minutes at sea level, 15 minutes above 5000 feet). Have an ice bath ready (ice and cold water nestled in a large bowl). When the eggs are finished boiling, transfer the to the ice bath. Let stand for about 3 minutes and then drain. Pat dry, peel, and quarter the eggs. Place the pieces in a large bowl.
To prepare the lavender mustard, add the dry lavender to the bowl of your food processor. Pulse 8-10 times or until the lavender is mostly powder. Add it to a small bowl, and fold in the mustard and mustard seeds. Reserve 2 tablespoons of the mustard, and cover the rest. Place in the refrigerator to use at a later time.
Add the 2 tablespoons of mustard to a small bowl with the mayonnaise. Season to taste with salt and black pepper. Add the mayonnaise to the bowl with the eggs. Very gently toss the eggs with the mustard, trying not to break up the eggs.
Cover and refrigerate the egg salad until you are ready to use.
To serve, layer the egg salad on toasted bread. Top with a small salad made up of greens and herbs. Sprinkle the salad with dried lavender, cracked black pepper, and flaky sea salt.