Preheat the oven to 400℉.
Marinate the chicken thighs with garlic, oregano, salt, paprika, 1/4 teaspoon of ground black pepper, and 1/2 tablespoon of lemon juice. Let sit for 5 minutes.
Grill the chicken in the oven for 25 minutes, until both sides are browned and cooked through evenly.
In the meantime, make the dressing: In a small bowl, whisk together olive oil, mustard, honey, 1 tablespoon of lemon juice, and 1/4 teaspoon of ground black pepper.
Allow the chicken to cool down and slice into thick strips (see images for reference).
On a large plate, assemble chicken together with romaine lettuce, cucumber, cherry tomatoes, red onion, and avocado.
Drizzle dressing all over and toss everything together. Sprinkle some parsley and serve immediately.