Sprinkle roast with salt and pepper. In a large skillet, heat oil over medium-high heat; brown meat. Transfer meat to a 5- or 6-qt. slow cooker. Add beer to skillet, stirring to loosen browned bits from pan; pour over meat. In a large bowl, combine jalapenos, onion, garlic powder and chili powder; pour over meat. Cook, covered, on low until tender, 6-8 hours., Remove roast; shred with 2 forks. Strain cooking juices. Reserve vegetables and 2 cups juices; discard remaining juices. Skim fat from reserved juices. Return beef and reserved vegetables and cooking juices to slow cooker; heat through. If desired, serve with optional ingredients.