Slice the chicken breast into thin, bite-sized strips for even cooking.
In a small bowl, combine the ground cumin, coriander, turmeric, garlic powder, sea salt, and black pepper to create the shawarma spice blend.
Toss the chicken strips with half of the olive oil and the spice mixture until every piece is thoroughly coated.
Heat the remaining olive oil in a cast-iron skillet over medium-high heat and sear the chicken until it is golden brown and cooked through.
While the chicken cooks, dice the cucumber and tomato, and finely mince the red onion.
Toss the diced vegetables with the lemon juice in a small bowl to create a bright, fresh salad.
In a separate small ramekin, whisk the tahini with a teaspoon of warm water until it reaches a smooth, pourable consistency.
Assemble the bowl by placing the warm basmati rice at the bottom, topping with the spiced chicken and the fresh salad, then finishing with a drizzle of the creamy tahini sauce.