Spray slow cooker with nonstick cooking spray (or use a slow cooker liner).
Pour in jar of spaghetti sauce.
Get out two shallow bowls.
In one bowl, whisk together egg and milk (add in any salt & pepper to taste).
In a second bowl, mix together panko bread crumbs with garlic powder, oregano and basil.
In a large skillet, begin heating up the vegetable oil (over medium-high heat).
You want to get your skillet hot before adding chicken to it.
Dip each chicken breast into the milk mixture.
Then roll it around in the seasoned bread crumbs.
Do each breast one at a time.
Then add chicken to hot skillet.
Continue with the rest of the chicken. You aren't cooking them.
All you want is to create a nice golden brown crust on both sides of the chicken breasts. If necessary, add a bit more oil to the pan.
After browning both sides, add chicken to the crockpot on top of the sauce.
Cover and cook on low for about 6-8 hours.
About 10-15 minutes before serving, sprinkle with shredded mozzarella cheese.
Cook spaghetti at this time
Cover again and allow cheese to melt.
Serve with spaghetti