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.
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.
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.