In a large skillet, heat the olive oil over medium heat. Season the chicken thighs well with salt and pepper., then sear them on each side for about 2-3 minutes until they're golden brown. Don't worry about cooking them through – they'll have plenty of time for that later!
Toss the seared chicken into your slow cooker.
In the same skillet (hello, flavor!), throw in the onion, garlic, and celery. Continue cooking until your kitchen smells amazing and the onion starts to look translucent. Add the carrots and potatoes, giving everything a good stir for another couple of minutes.
Dump all those lovely veggies into the slow cooker with the chicken.
In the pot, pour the chicken broth and white wine. Add the dried thyme and oregano, and season with salt and pepper according to your taste.
Cover and let it do its thing on LOW for 6-7 hours, or HIGH for 3-4 hours if you're in a rush.
About 30 minutes before you're ready to eat, mix the cornstarch with water in a small bowl until it's smooth. Stir this slurry into the stew along with the frozen peas. This will help thicken things up nicely.
Be sure to taste and adjust the seasoning if necessary before serving, and then sprinkle with fresh parsley for color and freshness.