Over medium high heat in a dutch oven or large stock pot add the ground beef, kosher salt, chili powder, oregano and cumin. Cook until no longer pink, about 6-7 minutes.
Stir in onion, jalapeños and tomato paste. Cook for several minutes. Stir in tomatoes and their juices. Reduce heat to low and cook for 20 minutes.
Add diced potatoes and carrot, stir and continue cooking for another 20 minutes. Stir occasionally and add some water if it gets too thick and does not scorch bottom of pot.
Assemble by spreading some refried beans on each tostada shell and top with ground beef mixture. Add chopped cabbage, cheese, creama, pickled red onion and chopped cilantro.
Notes
A little information for you on the two different oreganos: Mexican oregano is a relative of Lemon Verbena and is native to Mexico. Similar in that it’s pungent like Mediterranean oregano, Mexican oregano has notes of mild licorice and citrus. Mediterranean oregano is a member of the mint family and most often is used in Greek and Italian recipes. Mediterranean oregano is the one most found in spice racks and supermarkets.
If making your own corn tostada shells: To Bake: Preheat oven to 300°F. Place the corn tortillas in a single layer on a baking sheet and spray each side with cooking spray. Bake for 20-30 minutes until crispy, turning once. To Fry: Over high heat in a skillet add oil to reach 1/2 inch up sides of pan. Add 2-3 tortillas at a time and working quickly, fry until golden and crispy, carefully turning. Drain on paper towels and set aside.