Preheat oven to 325°F
Pat the beef tip sirloin roast dry
Season all sides with salt, pepper, garlic powder, and onion powder
Heat oil in a large oven-safe skillet or roasting pan over medium-high heat
Sear the roast on all sides until browned
Remove from heat
Add sliced onions, carrots, and potatoes if desired
Pour in beef broth or water to cover the bottom of the pan
Cover tightly with a lid or foil
Roast in the oven until the internal temperature reaches 135°F for medium-rare, 145°F for medium, or 160°F for well done
Check the temperature with a meat thermometer in the thickest part
Remove from the oven and let rest for 15 to 20 minutes
Slice against the grain
Serve warm