pre-heat oven to 400 degrees and line a baking pan with foil.
Add olive oil to a large skillet over medium heat. Add onion, chili powder, and salt and cook for 3 minutes. Add garlic and cook for another 2 minutes, until onions are browning.
Add chicken, chipotle chiles, adobo sauce, and oregano to skillet and stir to combine. Mix in salsa and cook for about 5 minutes.
Stir in rice and cook until rice is heated through.
Place a flour tortilla on a plate or work surface. Scoop about ¾ cup of the chicken filling into the center, sprinkle with cheddar cheese and add sliced olives (if desired). Fold the bottom edge of the tortilla tightly over the filling. Fold in the sides and then fold the top down to completely cover filling. Place on foil-covered baking sheet and repeat with remaining tortillas and ingredients. See recipe notes if you want to freeze some or all of the chimichangas.
Lightly brush tops of chimichangas with olive oil. Bake for 16-20 minutes until chimichangas are turning golden.
Serve with toppings like avocado, sour cream, tomatoes, additional cheese, and olives.