01 - Preheat oven to 375°F. Line a baking sheet with parchment paper.
02 - Cut croissants in half horizontally and arrange them, cut side up, on the baking sheet.
03 - In a medium bowl, whisk together eggs, milk, salt, and pepper until well combined.
04 - Melt butter in a nonstick skillet over medium-low heat. Pour in egg mixture and gently scramble, stirring with spatula, until just set but still slightly creamy. Remove from heat.
05 - Place a slice of ham and cheese on bottom half of each croissant. Top with generous spoonful of scrambled eggs. Add tomato, avocado, and chives if desired.
06 - Replace croissant tops and gently press down.
07 - Warm assembled sandwiches in oven for 5-7 minutes, or until cheese is melted and croissants are crisp.
08 - Serve immediately.