Either spray the slow cooker with nonstick cooking spray or line with a liner.
Add diced tomatoes, onion, green bell pepper, chicken broth, chili powder, oregano, cumin, onion powder, garlic powder and green chilis to the slow cooker. Stir to combine
Add chicken thighs and stir. Cover and cook on low for 5 to 6 hours and on high for 3 to 4 hours.
Once done remove chicken and shred with two forks. Add back to the slow cooker and stir to mix with the remaining juices.
To warm the corn tortilla, use a dry-skillet over medium heat. Add a tortilla and heat for 15 to 30 seconds on each side or until warm and toasty brown spots on it.
To serve: top the tortilla with the chicken fajita mixture, 2 tablespoons of cheese and a squeeze of lime.