In a small sauce pan, bring water to a soft boil. Gently place eggs into water and softly boil for 7 minutes. Remove eggs from water and place into a bowl of chilled ice water. Allow to cool for several minutes.
While eggs are cooling, in a small bowl or pan, melt butter in a microwave or stove top. Brush bread slices with melted butter. Heat a grill pan over medium heat. Grill bread until toasted.
In a medium size bowl, mash together avocados, lemon, and Tajin. In a separate bowl, toss together arugula and a vinaigrette.
To plate, spread slices of bread with smashed avocados. Layer with arugula and torn pieces of prosciutto. Nestle egg into a bed of prosciutto. Slice egg open right before serving. Season with Kosher salt and pepper.
