Combine the Herbs de Provence, garlic salt and pepper on a dinner plate. Spoon flour onto second dinner plate. Coat each chicken breast in the herb mixture, then dredge well in flour.
Heat oil in a large skillet. Add chicken and cook over medium-high heat until chicken is golden brown on both sides (approximately 3-4 minutes per side). Cook chicken in two batches if necessary so as not to crowd the pan.
Place chicken in a large slow cooker and add remaining ingredients, except fresh thyme. Cover slow cooker and cook on high for 4 hours or on low for 8 hours. Chop fresh thyme and sprinkle on before serving, if desired.