Marinate the Chicken: In a medium bowl, whisk together the olive oil, lemon juice, minced garlic, oregano, salt, and pepper. Add the chicken breasts and turn to coat them completely. Let them marinate at room temperature for at least 15 minutes, or for up to 4 hours in the refrigerator.

Preheat the Grill: Heat your outdoor grill or indoor grill pan to a medium-high heat (around 200°C). Make sure the grates are clean to prevent sticking.

Grill the Chicken: Place the marinated chicken breasts on the hot grill. Cook for 6-8 minutes per side. The exact time will depend on the thickness of your chicken. The chicken is done when it's opaque all the way through and the internal temperature reaches 74°C. For accurate results, I always use a meat thermometer. You can find safe cooking guidance on the Food Standards Agency website.

Rest the Chicken: This is a critical step! Remove the chicken from the grill and place it on a cutting board. Let it rest for 5-10 minutes. This allows the juices to redistribute throughout the meat, ensuring it stays wonderfully moist.

Prepare the Vinaigrette: While the chicken is resting, make the dressing. In a small bowl or jar, combine the extra virgin olive oil, lemon juice, Dijon mustard, honey, and chopped parsley. Whisk vigorously or shake the jar until the dressing is well combined. Season with salt and pepper to your liking.

Assemble the Salad Base: In a large salad bowl, combine the chopped Romaine lettuce, halved cherry tomatoes, sliced cucumber, and thinly sliced red onion.

Slice the Chicken: After resting, slice the grilled chicken breasts against the grain into strips about 1cm thick.

Combine and Serve: Add the sliced grilled chicken and the sliced avocado to the salad bowl. Drizzle with about half of the vinaigrette and gently toss to combine. Serve immediately, with the remaining dressing on the side for those who want extra.