Preheat oven to 350º.
In a small mixing bowl, combine black beans and spices.
Cook toastada shells on a baking sheet for 3-5 minutes to crisp them up. Be careful not to burn them.
Spread each tostada shell with black beans and top with lettuce, salsa, Sweet Corn Guacamole (recipe below) and queso fresco. Or your favorite tostada toppings.
Sweet Corn Guacamole
Remove kernels from cob and place in pan. Over medium heat, roast the corn until it starts to caramelize. Set aside to cool. (Note: You also can roast the corn in the husk. Simply remove the silks and soak in water for about 10 minutes and then place on the grill, cooking until the kernels begin to color)
Place the avocado in a bowl and mash with a potato masher or back of a fork, leaving it somewhat chunky.
Add in the garlic, onion and jalapeño. Stir in the cooled corn kernels, cilantro, garlic, salt and pepper. Mix until combined.
Add the lemon juice and mix well.