Heat the oil in a large skillet over medium heat. Add a corn tortilla and cook it for 3-4 minutes per side, until crispy and golden brown.
Heat the leftover drained, rinsed black beans in a small saucepan over medium heat. Season with sea salt, freshly cracked pepper, garlic powder, and cumin to taste, and cook, stirring often, for 5-7 minutes, or until hot.
Heat the butter or oil in a large skillet over medium-high heat. Add the shrimp and season with sea salt, freshly cracked pepper, cumin, oregano, paprika, chili powder, and garlic powder to taste. Cook for 2-3 minutes, then flip them and cook for 1-2 minutes, or until done. Remove from heat. Drizzle with lime juice from ½ a lime. Side Note: I didn't measure the seasoning; I just sprinkled a little of each over the shrimp.
Layer the crisp tostada shell with sour cream, black beans, cooked shrimp, avocado, tomatoes, green onions, and cilantro.
Serve with the remaining ½ lime, cut into wedges, on the side. Enjoy!