Combine the sweet potato cubes, olive oil, garlic salt and taco seasoning, and mix until well blended. Spread evenly on a large greased baking sheet and roast the mix for about 20 to 25 minutes, turning the diced pieces halfway through, or until golden and tender.
Heat a large pan over medium heat. Add the canola oil, onions, ground beef, salt, pepper and garlic, cook for 5 minutes or until beef is cooked through. Set aside on absorbent paper to remove the excess grease.
Place a lettuce leaf in the bottom of each bowl and spread the beef over those, then top with all the toppings and mayonnaise.