Slice the chicken breast into thin bite-sized strips.
In a small bowl, combine the cumin, coriander, turmeric, garlic powder, sea salt, and black pepper.
Toss the chicken strips in the spice blend until evenly coated.
Heat the olive oil in a non-stick skillet over medium-high heat.
Add the chicken to the skillet and cook for 6-8 minutes, stirring occasionally, until the exterior is golden brown and the center is cooked through.
In a separate small dish, whisk together the tahini and lemon juice, adding a teaspoon of warm water at a time until a smooth, pourable consistency is reached.
Place the warm cooked brown rice in the center of a bowl.
Arrange the cooked chicken, diced cucumber, diced tomato, and sliced red onion over the rice.
Drizzle the lemon-tahini sauce over the entire bowl and serve immediately.