In a medium size pan add the refried beans, cumin, garlic, pepper, and water. Stir together. Warm on low heat.
Crispy Heart-Shaped Tostada Shells:
Cut Tortillas into Hearts - Place a corn tortilla on a plate or cutting board. With a small knife or kitchen-only scissors, cut each corn tortilla into the shape of a heart.
Cook Tortillas - Heat a small skillet on medium heat and add canola oil.To test if the oil is hot enough, using tongs, carefully dip just an edge of the tortilla in the oil and if it sizzles add the entire heart tortilla to the pan.
When the bottom side of the torilla turns a golden color, using tongs, carefully turn it over in the pan. Cook until each side of the tortilla is golden brown (about 3 or 4 minutes).
Transfer Cooked Tortilla to Paper Towel-Lined Plate - Using tongs, carefully transfer the tortilla from the pan onto a paper towel-lined plate. Set aside.
Repeat this process with the remaining heart-shaped tortillas.
Assemble the Tostadas:
Spread warm refried beans on top of the crispy tortilla shells. Top with a layer of salsa, and layers of shredded cheese, purple cabbage, tomatoes, cilantro, green onions, and chopped or shredded lettuce (optional).
Garnish:
As an option, add the sour cream to a pastry bag with your favorite decorative tip. Pipe the sour cream around the outside edges of the tostada so that it resembles the look of lace. Or make any decoration with the sour cream you would like.