Step 1: In a large bowl, toss the cubed chicken and shrimp with chili powder, cumin, garlic powder, salt, and pepper until evenly coated.
Step 2: Heat 1 tablespoon of olive oil in a large skillet or frying pan over medium-high heat. Add the seasoned chicken and cook for 4-5 minutes, or until browned and mostly cooked through. Add the shrimp and cook for another 2-3 minutes, until pink and cooked through. Remove the chicken and shrimp from the pan and set aside.
Step 3: In the same skillet, add the minced garlic and sauté for 30 seconds until fragrant. Add the fresh spinach, a handful at a time, and cook until wilted. Squeeze out any excess liquid from the spinach.
Step 4: Return the chicken and shrimp mixture to the pan with the spinach. Stir to combine all the ingredients. Remove from heat.
Step 5: Wipe out the skillet. Place one tortilla in the dry skillet over medium heat. Sprinkle about 1/4 cup of Monterey Jack cheese and 2 tablespoons of cheddar cheese over half of the tortilla. Spoon a generous portion of the chicken, shrimp, and spinach mixture over the cheese.
Step 6: Fold the other half of the tortilla over the filling. Cook for 2-3 minutes per side, or until the tortilla is golden brown and crispy, and the cheese is melted and bubbly. Press down gently with a spatula.
Step 7: Remove the cooked quesadilla from the pan, slice into wedges, and serve immediately with your favorite toppings like salsa, guacamole, or sour cream. Repeat with the remaining tortillas and filling.