In a small bowl, whisk together the ground cumin, coriander, turmeric, garlic powder, sea salt, black pepper, and 1 teaspoon of olive oil to create a marinade.
Slice the chicken breast into thin, bite-sized strips and toss in the spice marinade until every piece is evenly coated.
Heat the remaining 1 teaspoon of olive oil in a large skillet over medium-high heat.
Add the chicken to the skillet and cook for 6 to 8 minutes, stirring occasionally, until the chicken is golden brown and cooked through.
While the chicken is cooking, dice the cucumber and red onion, and halve the cherry tomatoes.
Toss the diced vegetables in a small bowl with a splash of the lemon juice.
In a separate small dish, whisk together the Greek yogurt, tahini, and the remaining lemon juice until the sauce is smooth and creamy.
Assemble the bowl by placing the warm cooked brown rice at the base, then topping it with the shawarma chicken and the fresh vegetable salad.
Finish the dish by drizzling the lemon-tahini sauce over the top and serve immediately.