First, cook chicken. To do this, combine chicken, chicken broth, salt and pepper. Instant Pot directions: Cook on high pressure for 10 minutes. Let natural release for 10 minutes. Remove chicken and shred with two forks. Slow cooker directions: Cook on low for 7 hours or on high for 4 hours. Remove and shred with two forks. Oven directions: Use aluminum foil to cover 8x8 baking pan. Let foil hang up over sides. Place chicken and broth mixture in pan. Fold aluminum foil up so that chicken is entirely covered with foil. Bake at 350 degrees for 45 minutes, or until thickest part of chicken is no longer pink. Shred with two forks.
In a medium sized sauce pan over medium heat, add all of the sauce ingredients, except for the corn starch. Bring to a simmer, reduce heat to low, and let simmer for 10 minutes. Use an immersion blender to blend sauce. While constantly stirring, sprinkle corn starch over top of sauce. Let simmer for 2 more minutes, then remove from heat.
Preheat oven to 400 degrees. Spray a 9x13 baking dish with cooking spray.
In a small skillet, heat olive oil over medium-high heat. Add chopped red pepper and diced onion. Saute until softened, about 6-7 minutes. Add garlic and saute for 1 more minute, remove from heat.
Stir together shredded chicken, cooked vegetables, and 2/3 cup of sauce in a small bowl.
Place about ½ cup of chicken mixture in a tortilla. Roll and place seam side down in prepared baking dish.
Use remaining sauce to cover top of tortillas. Cover with aluminum foil and bake for 20 minutes.
Remove from oven. Sprinkle feta, cilantro, and red onion over top of enchiladas before serving. You can adjust the amount of feta, cilantro, and red onion to your tastes. I usually cover the top with about ¼ cup feta, 2 tbsp cilantro, and 2 tbsp of red onion, then leave the rest for each person to add ad they would like.