In a large skillet, heat the canola oil until shimmering. Add the onion, bell pepper, garlic and chili powder and season with salt and pepper. Cook over high heat, stirring, until softened and browned in spots, about 5 minutes. Add the beef and gravy and cook, stirring, until just heated through, 1 minute. Serve the beef and vegetables in warm tortillas with salsa, sour cream and cilantro.