Heat a skillet over medium heat. Coat a corn tortilla with cooking spray on both sides and place it into the skillet. Cook for 3-4 minutes on each side until crispy and golden brown. Heat the leftover drained and rinsed black beans seasoned with sea salt, freshly cracked pepper, garlic powder, and cumin, to taste, in the microwave for 30 seconds or until warm.
Place the skillet coated with cooking spray back on the stove 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. Side Note: I didn't measure the seasoning, I just sprinkled a little bit of each onto the shrimp. Cook for 2-3 minutes then flip the shrimp and cook for another 1-2 minutes, or until done. Remove from heat.
Layer the tostada shell with sour cream, black beans, cooked shrimp, avocado, tomatoes, green onions, and cilantro. Serve immediately. Enjoy!