Whisk the cumin, smoked paprika, turmeric, garlic powder, sea salt, and black pepper in a small bowl, then toss with the sliced chicken breast until evenly coated.
Heat the olive oil in a non-stick skillet over medium-high heat and sauté the chicken until it is golden brown and cooked through, approximately 6-8 minutes.
In a separate small bowl, combine the diced cucumber, halved cherry tomatoes, and minced red onion with half of the lemon juice to create a fresh salad.
Stir the remaining lemon juice into the Greek yogurt until the mixture is smooth and slightly thinned.
Place the warm cooked brown rice at the base of a bowl and top it with the spiced shawarma chicken and the cucumber-tomato salad.
Finish the dish by drizzling the lemon-yogurt sauce over the top and serve immediately.