Preheat the oven to 400°F (200°C) and line a sheet pan with parchment paper. Lightly spray both sides of each corn tortilla with cooking spray. Arrange the tortillas on the sheet pan in an even layer and bake for 4-5 minutes. Flip and bake for another 4-6 minutes, keeping a close eye on them during the last few minutes, as they can go from perfectly crisp to burnt quickly. Remove from the oven and set aside.

In a mixing bowl, combine the shrimp, just half the oil, chili powder, cumin, and a dash of salt. Mix until evenly coated.

Heat a skillet over medium-high heat and add the remaining oil. Add the shrimp and cook for 2-3 minutes per side, until pink and opaque. Set aside to cool.

Once cool enough to handle, transfer the shrimp to a cutting board and chop into bite-sized pieces.

Spread about 2 tablespoons of guacamole onto each tostada and top with shrimp. Feel free to add cilantro, lime juice, or other low-calorie toppings.