First marinate the pork. Combine the pork, oil, lime juice, onion and garlic in a bowl. Mix the cumin, cinnamon, salt, allspice, cayenne and a few grinds of black pepper in a small dish. Add to the pork mixture and marinate for 30 minutes at room temperature.

While the pork marinates, crisp the tortillas. Preheat the oven to 375°F. Place the tortillas on a baking sheet in a single layer and bake until crisp, 8 to 12 minutes. Remove from the oven and set aside.

Next, make the salsa. In another bowl, combine the diced tomato, scallions, jalapeño and cilantro. Season to taste with salt and pepper and set aside.

To cook the pork, heat a large pan over medium-high heat, add the pork and cook just until done, about 2 minutes. Remove from the pan with a slotted spatula and set aside. Add the refried beans to the liquid that remains in the pan from the pork, combine well and heat through.

To assemble the tostadas, spread about 1/4 of the refried beans on each tortilla and top with a serving of pork. Top with lettuce, tomato salsa, crumbled queso and a dollop of sour cream.