01 - Set oven to 425°F and line a baking sheet with parchment paper.
02 - Whisk flour, baking powder, baking soda, sugar, and salt in a large bowl. Cut in cold butter until the mixture forms coarse crumbs.
03 - Pour in cold buttermilk and gently combine until just mixed. Transfer dough to a floured surface, pat into a 1-inch rectangle, and fold in thirds. Turn, repeat folding twice for flaky layers.
04 - Cut 4 biscuits with a 3-inch cutter. Place on prepared sheet, brush tops with buttermilk, and bake for 14–16 minutes until golden brown. Cool slightly.
05 - Pat chicken breasts dry and season generously with Cajun spice. Heat olive oil in a skillet over medium-high. Cook chicken for 5–6 minutes per side until golden and cooked through (internal temperature 165°F). Rest 5 minutes, then slice.
06 - Whisk eggs, milk, salt, and pepper. Melt butter in a nonstick skillet over medium heat. Pour in eggs, gently scramble until just set.
07 - Split warm biscuits; layer with scrambled eggs, sliced Cajun chicken, cheese, and green onions if desired. Cap with biscuit tops and serve immediately.