Preheat the oven to 400 degrees F. Heat oil in a large skillet set over medium heat.
Add onion, bell pepper, and jalapeño to the pan. Season with cumin, paprika, salt, and pepper, then cook for 5-6 minutes, or until onions are translucent. Add garlic and cook for 30 seconds, until fragrant.
Scoop about ½ cup chicken and place on a flour tortilla. Top with cheese, then roll tightly into a burrito. Place the rolled burrito seam side down on a parchment-lined baking sheet. Repeat with remaining ingredients, forming 6 chimichangas.
Brush the tortillas with melted butter. Bake for 20-25 minutes, or until chimichangas are golden brown and crispy.