Combine the Herbs de Provence, garlic salt, and pepper on a dinner plate. Spoon flour on to 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 (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.
Sprinkle with fresh thyme before serving, if desired.