1. Season 8 bone-in, skinned chicken thighs and/or drumsticks with 1/2 tsp. each kosher salt and ground black pepper. In a very large nonstick skillet, heat 1 Tbsp. olive oil over medium-high heat Add the chicken and cook about 4 minutes per side or until browned. Transfer to a 5- to 6-quart slow cooker.
2. In the same skillet, cook 1 large sliced yellow onion over medium heat until tender, about 5 minutes. Add 3 large sliced garlic cloves and cook 1 minute more. Add to the slow cooker with one 14.5-oz. can diced tomatoes, 1/2 cup reduced sodium chicken broth, and 1 Tbs. red wine vinegar. Cover and cook on high for 2 1/2 hours or low for 5 hours. Stir in 1 bunch coarsely chopped Swiss chard (5 cups), 1/2 tsp. chopped fresh sage, and 1/2 tsp. kosher salt. Cover and cook 10 minutes more. Serve with crusty bread.