Preheat the grill to medium-high heat. Season the chicken breasts with olive oil, garlic powder, salt, and black pepper.
Grill the chicken for 6-7 minutes per side, or until it reaches an internal temperature of 165°F (74°C). Remove from the grill and let it rest for a few minutes before slicing it into strips.
In a large salad bowl, combine the mixed greens, sliced cucumber, halved cherry tomatoes, red onion, and avocado slices.
Add the grilled chicken strips to the salad and toss gently to combine.
Drizzle with lemon juice and a little extra olive oil if desired. Toss again and serve immediately.
Notes
This salad is easily customizable by adding other vegetables or a sprinkle of cheese like feta or Parmesan. You can also add a handful of nuts or seeds for extra crunch.