In a large frying pan over medium heat, swirl in the oil. Brown the ground turkey. Add the chopped onions and cook 2 minutes until translucent. Stir in the garlic powder, tomato sauce, ketchup, brown sugar, vinegar, Worcestershire sauce, and black pepper. Turn the heat down to low and simmer uncovered, stirring occasionally, about 10 minutes until thickened. Season with salt to taste and add hot sauce if desired for a little heat. Serve a heaping spoonful of the sloppy joe mixture on lightly buttered toasted hamburger buns. Top with cheddar cheese and green onions, if desired, and hot sauce on the side. Repeat with remaining buns. Serve promptly.