Precut butternut squash is usually sold in a 20-ounce package of large cubes (5 cups of 1- to 2-inch pieces) or in a 16-ounce package of smaller diced squash (3 cups of 1/2-inch pieces). If you can only find the smaller cubes for this recipe, you'll need to buy two 16-ounce packages to have 5 total cups of squash and reduce the roasting time by 5 to 10 minutes. Or, you can prep your own cubes of squash from a whole, peeled and seeded butternut squash.
You can make your own tostadas using fresh corn tortillas. Heat about 1/2 inch canola, peanut or avocado oil in a small skillet over medium heat. Add a corn tortilla and cook for 1 to 2 minutes. Flip and cook until crisp, 1 to 2 minutes. Drain on paper towels. Repeat until all tortillas are cooked, reducing heat, if necessary, to prevent the oil from smoking or splattering.