Place the ground sirloin in a heavy bottom skillet, and cook meat to a golden brown, with no pink left. Remove cooked sirloin to a paper towel lined plate, and drain fat. Place the chopped onion in the skillet, and saute for 2 minutes. Return the meat to the skillet, and stir well with onion. Add the taco seasoning, garlic salt, sugar, salsa, ranch beans, and cheese, stir, and let simmer all together for about 20 minutes.
While the taco meat is simmering, cut out the Tortillas; using a large biscuit cutter, or round cookie cutter (about a 4 inch cutter - see link) cut out the rounds, and place them on the back of a muffin tin, between the muffin cups. Bake at 350 for 10 minutes. Remove from oven and cool slightly. Fill with met filling, and place in oven and bake for 4 minutes. Remove from oven, and top with chopped tomatoes, and green onions. Serve with salsa, and sliced limes. Enjoy!