Place the chicken thighs at the base of the slow-cooker pan. Sprinkle the chicken with the minced garlic and oregano. Season with salt and pepper, a pinch of each.
Sporadically place the kalamata olives throughout the slow-cooker pan. Lay the lemon slices over the chicken, making sure each thigh has been covered with the lemon slices. Finally, drizzle the tablespoon of olive oil over the chicken and lemon slices.
Set the slow-cooker to low, and allow the chicken to cook for about 6 hours. Cooking times may vary depending on the slow-cooker. The chicken is done when it has reached 165°F.
When the chicken is almost done, cook the orzo according to package instructions.
Serve a portion of chicken (olives and lemon slices included) over each serving of orzo. Drizzle with olive oil and sprinkle with crumbled feta.
While the recipe suggests cooking this dish on the low setting of the slow-cooker, (which yields the best results) you can set the cooker to high as well. If cooking on high, check the chicken after 3 hours.