Pat the chicken thighs dry and sprinkle evenly with 1 teaspoon salt and 1/2 teaspoon of the black pepper.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add half the chicken and brown about 3 minutes per side; transfer to a plate.
Add the remaining 1 tablespoon oil to the skillet and brown the remaining chicken the same way; transfer to the plate.
Spray the inside of the slow cooker with nonstick spray. Place the peeled, cubed potatoes in an even layer in the bottom of the cooker and set the browned chicken on top.
In a mixing bowl, whisk together the chicken broth, lemon juice, flour or cornstarch, and minced garlic until smooth.
Pour the broth mixture over the chicken and potatoes in the slow cooker. Sprinkle the remaining 1/2 teaspoon black pepper over the top.
Cover and cook on low for 6 hours or on high for 4 hours, until the chicken is cooked through and potatoes are tender.
Garnish with lemon slices and serve.