Place the egg in a small pot of water, bring to a boil, then cover and remove from heat for 10 minutes before peeling and slicing.
Season the chicken breast with half the salt, pepper, and garlic powder.
Heat olive oil in a skillet over medium-high heat and sear the chicken for 5-6 minutes per side until the exterior is golden and crispy.
While the chicken rests, whisk together the Greek yogurt, Dijon mustard, lemon juice, and remaining spices in a small bowl to create the dressing.
Chop the romaine lettuce, halve the cherry tomatoes, and slice the cucumber and avocado.
Assemble the salad by layering the greens, vegetables, sliced egg, and sliced chicken, then drizzle with the creamy dressing.