Spray a 6-quart slow cooker generously with cooking spray.
Place the chicken thighs in the prepared slow cooker in an even layer.
Pour the salsa over the chicken.
Sprinkle the chili powder, cumin, paprika, garlic powder, onion powder, dried oregano, salt, and pepper over the salsa and chicken.
Stir gently to combine so the spices and salsa coat the chicken; try to submerge the chicken as much as possible.
Cover and cook on high for 210 minutes (3½ to 5 hours) or on low for 240–360 minutes (4–6 hours), until the chicken shreds easily.
Turn off the slow cooker, remove the chicken to a cutting board, discard any excess fat, and shred with two forks or cut into pieces with a knife.
Return the shredded chicken to the slow cooker, stir gently to combine with the sauce, and taste; adjust seasoning if desired.
Serve over cooked rice or in tacos and top with roasted corn and peppers and your preferred toppings.