1. Preheat oven to 400°. Mix 1 tbsp. oil with melted butter, and brush some onto a baking sheet. Heat remaining 1 tbsp. oil in a large frying pan over medium heat; add chile, onion, nopales, and salt; and cook, stirring often, until vegetables soften and start to brown, about 5 minutes.
2. Put 2 tbsp. each cheese and beans and about 1/4 cup of the vegetable mixture onto center of a tortilla. Fold in sides and roll up like a burrito. Set chimichanga onto greased baking sheet, seam side down. Fill remaining tortillas and space about 2 in. apart on pan. Brush remaining butter mixture over chimichangas.
3. Bake, turning halfway through, until browned and crisp, about 20 minutes. Cut chimichangas in half diagonally and serve with salsa and guacamole.
*Buy cut and cleaned nopales (cactus pads) at a Latino market.
Make ahead: Through step 2 up to 5 hours, chilled; bake about 5 minutes longer.
Note: Nutritional analysis is per 2-piece serving.