Preheat oven to 375''F. Melt butter in medium skillet over medium heat. Add chicken, oregano, salt and black pepper; cook and stir 3-5 minutes. Remove chicken from skillet with slotted spoon; place in bowl and reserve.
Pour oil into same skillet to 1/4" depth; heat oil over medium-high heat. Cook 1 tortilla in hot oil about 1 minute or until crisp. Remove tortilla from skillet; drain on paper towels and place on large baking sheet.
Repeat with remaining tortillas. Spoon 1/4 of chicken mixture evenly over each tortilla. Top each with 2 tablespoons tomato, 2 tablespoons onion, 1 tablespoon green pepper, 2 tablespoons pizza sauce and 1/4 cup cheese.
Bake 5 minutes or until cheese melts. Garnish with chili peppers, if desired.