Prepare all ingredients.
Heat olive oil in a skillet over medium heat.
Sear the chicken breasts for 2-3 minutes on each side.
Place the chicken in the crockpot.
Add chopped onion and minced garlic.
Layer mixed vegetables over the chicken.
Pour chicken broth over all.
Sprinkle thyme, salt, and pepper.
Cover and cook on low for 6-8 hours.
Thicken sauce with cornstarch if desired.