First, prepare the chicken by butterflying each chicken breast. Slice it horizontally without cutting all the way through, then open it like a book and gently pound it to an even thickness using a meat mallet or rolling pin. Season both sides evenly with the garlic powder, salt, and black pepper, ensuring every piece is well coated for maximum flavour.
Next, heat a grill pan over medium-high heat and melt the butter, allowing it to coat the surface of the pan. Place the seasoned chicken onto the hot grill and cook for 4–5 minutes without moving it so beautiful grill marks develop. Flip and cook for another 4–5 minutes, or until the chicken reaches an internal temperature of 74°C (165°F). Transfer to a plate and let it rest for 5 minutes before slicing into strips.
Meanwhile, prepare the homemade lemon dressing. In a small bowl or jar, whisk together the extra virgin olive oil, fresh lemon juice, honey, salt, and freshly ground black pepper until smooth and well combined. Taste the dressing and adjust the seasoning if needed by adding a little more lemon juice for brightness or honey for sweetness.
In a large serving bowl, combine the baby spinach and lettuce as the base of the salad. Add the sliced cucumber, cooked beetroot, and drained pickled red onions, spreading them evenly over the greens to create a colourful and well-balanced salad.
Finally, arrange the sliced grilled chicken over the vegetables and sprinkle the crumbled feta cheese evenly on top. Drizzle the homemade lemon dressing over the salad just before serving, then gently toss everything together until lightly coated. Serve immediately while the chicken is still warm for the best flavour and texture.