Prepare the Shrimp: Peel and devein the shrimp, then pat them dry thoroughly with paper towels.
Season the Shrimp: Place the shrimp in a bowl and add 2 tablespoons of olive oil, the Cajun seasoning, chilli flakes, salt, and pepper. Toss well until the shrimp are evenly coated with the seasoning.
Cook the Shrimp: Place a large skillet or pan over medium-high heat and add the seasoned shrimp. Cook for about 1 minute per side, until golden and cooked through. Remove from the pan and set aside.
Prepare the Avocado: Halve the avocados and scoop the flesh from the skins into a bowl. Add the lemon juice, chilli flakes, salt, and pepper. Mash with a fork until smashed and combined, then set aside.
Slice the Bread: Cut the ciabatta into 8 thick slices.
Toast the Bruschetta: Heat 2–3 tablespoons of olive oil in a large pan over medium-high heat. Add the bread slices and cook for 30 seconds to 1 minute per side, until golden and toasted.
Assemble the Bruschetta: Spread a generous amount of the smashed avocado over each toasted ciabatta slice. Top with the cooked shrimp.
Finish and Serve: Sprinkle the bruschetta with chopped chives and finish with a squeeze of lemon. Serve immediately.