Slice the chicken breast into thin, bite-sized strips and place them in a medium mixing bowl.
Add the olive oil, cumin, coriander, turmeric, garlic powder, sea salt, and black pepper to the chicken and toss until every piece is thoroughly coated in the spice blend.
Heat a large non-stick skillet over medium-high heat and add the seasoned chicken strips in a single layer.
Sear the chicken for 6-8 minutes, turning occasionally, until the exterior is golden brown and the meat is cooked through.
While the chicken cooks, prepare the tahini sauce by whisking together the tahini, lemon juice, and water in a small bowl until the consistency is smooth and pourable.
In a separate small bowl, combine the diced cucumber, tomato, and red onion to create a quick fresh salad.
To assemble, place the warm cooked basmati rice in the bottom of a bowl and top with the seared shawarma chicken and the vegetable salad.
Finish the dish by drizzling the creamy tahini sauce over the top and serve immediately.