Prep the chicken: Shred or dice cooked chicken into bite-size pieces. Pat dry with a paper towel so the sauce clings well.
Make the Buffalo dressing: In a large bowl, whisk Greek yogurt, light mayo, Buffalo sauce, lemon juice, garlic powder, and a pinch of salt and pepper. Taste and adjust heat by adding more Buffalo sauce if you like it spicier.
Toss the chicken: Add chicken to the dressing and stir until evenly coated.
Fold in celery, carrots, red onion, and half the green onions.
Build the salad base: In another bowl, toss greens with olive oil, a squeeze of lemon, and a pinch of salt and pepper. Add tomatoes and cucumber.
Assemble: Spoon the Buffalo chicken mixture over the greens. Top with blue cheese or feta, remaining green onions, and avocado slices if using.
Finish and serve: Drizzle a little extra Buffalo sauce over the top if you want more heat.
Serve immediately, or keep components separate for meal prep.