In medium skillet, carmelize onions by cooking in olive oil over medium heat. As they cook down and start to dry out, sprinkle in a tablespoon of water to help soften and steam onions. Season with salt and pepper. Let onions continue to caramelize while preparing rest of ingredients. Onions should be soft and golden brown.

In a small bowl, stir together mayonnaise and sriracha and set aside.

Preheat oven to 375°. Line a baking sheet with foil and spray with non stick cooking spray. Cut bacon slices into thirds and arrange on baking sheet. Bake for 20-30 minutes, checking bacon often for doneness. Bacon will cook very quickly in the last few minutes. Once bacon is crispy, transfer to a paper towel lined plate to drain.

In a large mixing bowl, whisk together eggs, milk, and 1/2 teaspoon kosher salt. Melt one tablespoon of butter in a large non stick skillet and swirl. For the smoothest eggs, use a fine mesh strainer to strain egg mixture into skillet and discard the small hard pieces (chalazae and meat spots) that don't blend into the eggs. Cook eggs over medium low to medium heat gently pushing egg curds as they form. Cook until almost set and stir in chives. Eggs should be tender and soft scrambled.

Lightly butter and toast buns. Assemble breakfast sandwiches by starting with avocado, followed by bacon, eggs, cheese slice, caramelized onions, and finish by spreading top bun with spicy mayo. Wrap in waxed paper if desired and serve.