In a small bowl, combine the ground cumin, coriander, turmeric, garlic powder, sea salt, and black pepper to create the shawarma spice blend.
Slice the chicken breast into thin, bite-sized strips and toss them thoroughly with the spice blend until every piece is evenly coated.
Heat the olive oil in a non-stick skillet over medium-high heat. Add the chicken strips and sear for 5-7 minutes, turning occasionally, until the edges are crispy and the chicken is cooked through.
While the chicken is searing, whisk together the tahini and lemon juice in a small ramekin, adding a teaspoon of water if needed to reach a smooth, pourable consistency.
Prepare the bowl base by layering the chopped romaine lettuce and cooked quinoa in a large serving bowl.
Top the greens with the diced cucumber, halved cherry tomatoes, and finely diced red onion for a fresh crunch.
Place the warm, crispy shawarma chicken over the vegetables, drizzle the lemon-tahini dressing over the entire bowl, and garnish with freshly chopped parsley.