1. Grate rind and squeeze juice from lemon to measure 1 teaspoon and 1 tablespoon, respectively. Place lemon rind in a small bowl. Cover and refrigerate. Combine lemon juice, onion, and next 3 ingredients (through tomatoes) in a 5-quart electric slow cooker.
2. Sprinkle chicken with pepper. Heat a large nonstick skillet over medium-high heat. Add oil to pan; swirl to coat. Place half of chicken in pan; cook 3 minutes on each side or until browned. Place chicken in slow cooker. Repeat procedure with remaining chicken. Cover and cook on LOW for 4 hours or until chicken is done.
3. Place chicken thighs on plates. Stir reserved lemon rind into sauce. Serve sauce over chicken. Garnish with rosemary and parsley, if desired.
Flavor Tip: Piquant, sharp, and tangy are just a few words to describe capers. Use capers sparingly to infuse sauces, salads, pizzas, dressings, and pasta or vegetable dishes with flavor.