Japanese Sandwich (Mixed Sando)

Bahan-bahan (3 porsi)

• shokupan (Japanese milk bread)
• salted butter ((at room temperature; I use spreadable butter))
• Japanese Kewpie mayonnaise
• mustard ((optional; I skipped it as my family is not fond of it))
• ⅛ onion
• ½ (5-ounce) can albacore tuna (preferably packed in olive oil)
• 2 Tbsp Japanese Kewpie mayonnaise
• freshly ground black pepper
• Diamond Crystal kosher salt
• 3 large large eggs (50 g w/o shell)
• ¼ tsp sugar
• ¼ tsp Diamond Crystal kosher salt
• ⅛ tsp freshly ground black pepper
• 2 tsp milk
• 2 Tbsp Japanese Kewpie mayonnaise
• 2 leaves iceberg lettuce ((trimmed to the size of a shokupan slice))
• 2 slices ham
• 2 slices Swiss cheese
• 6 slices Japanese or Persian cucumber ((thinly sliced diagonally))