01 - Preheat oven to 375°F. Line a baking sheet with parchment paper.
02 - Slice croissants in half horizontally. Arrange halves cut side up on prepared baking sheet.
03 - Whisk together eggs, milk, salt, and pepper in a medium bowl until thoroughly combined.
04 - Melt butter in nonstick skillet over medium-low heat. Pour in egg mixture and scramble gently with spatula until just set but still slightly creamy. Remove from heat.
05 - Place ham and cheese slice on bottom half of each croissant. Top with scrambled eggs. Add tomato, avocado, and chives if using.
06 - Replace croissant tops and press gently to secure.
07 - Bake assembled sandwiches for 5–7 minutes until cheese melts and croissants are heated through and crisp.
08 - Serve immediately while warm and crisp.