In a bowl, squeeze limes and stir in olive oil, cilantro, chipotle powder, paprika, cracked pepper, cumin, and chopped serranos; stir in shrimp. Let this set in the fridge for about 10 minutes
While the shrimp is marinating, prepare your tostadas. Slice avocado, shred cabbage, prepare mango salsa (if you haven't done this ahead of time). Heat up black beans and pre-heat your grill.
Place on the grill and pour the remaining marinade over the shrimp. Cook for 5-7 minutes until opaque.
For the tostadas, place avocado, then black beans. Top with cabbage, mango salsa and add shrimp. Garnish with cojita cheese and add a little more cilantro if desired. Enjoy!