Remove stems of mushrooms and discard or reserve for another use. With a spoon, scrape black gills from portobello caps and discard. Brush outside of caps with canola oil and place on a microwave-safe platter. Chop meat from package into approximately 1/2-inch pieces. Mix chopped meat and au jus or gravy together with peas and carrots. Spoon mixture into mushroom caps, dividing equally. In a medium bowl, mix together hot cooked rice and cheddar cheese and spread evenly over tops of filled mushrooms. Cover with wax paper and cook in microwave oven on high for 10-12 minutes until mushrooms are softened and thoroughly heated through, turning dish occasionally. Sprinkle with chopped chives.