Preheat the oven to 400°F (200°C). Place tostada shells on a baking sheet and warm in the oven for about 5 minutes, or until slightly crispy.
In a skillet over medium heat, add the black beans, corn, ground cumin, chili powder, salt, and pepper. Cook for about 5-7 minutes, stirring occasionally until heated through.
While the beans and corn are cooking, prepare the fresh toppings. Dice the avocado, halve the cherry tomatoes, and shred the lettuce. Finely chop the red onion and cilantro.
Remove the tostada shells from the oven. Spoon the black bean and corn mixture evenly onto each tostada shell.
Top each tostada with diced avocado, cherry tomatoes, shredded lettuce, red onion, and cilantro.
If desired, sprinkle feta cheese or queso fresco on top. Serve with lime wedges and hot sauce for a zesty kick.