In a small bowl, combine all ingredients for spice mix, set aside.
Peel and de-vein thawed shrimp, then chop very fine or use a food processor to grind to similar consistency of the ground pork. In a large bowl, combine the ground pork and shrimp. Reserve 1 Tablespoon of spice mix, and pour the rest into the pork/shrimp mixture, along with 2 Tablespoons of the lime juice and 1 1/2 Tablespoons of the oil. Stir to combine, cover, and place in the fridge to marinate for an hour.
Remove pork/shrimp from fridge. Using a large skillet (preferably a cast iron skillet) saute the pork/shrimp mixture over medium heat, stirring frequently, until cooked through and lightly browned (about 15 minutes). Place cooked mixture in another large bowl, set aside, and return skillet to heat. Add the other 1 1/2 tablespoon of oil to skillet, along with the shallots and garlic, saute about 2 minutes, until slightly softened. Add the frozen corn kernels and continue to saute, another 2 minutes, then add the bell peppers, poblano pepper, black beans, and reserved Tablespoon of spice mix and continue to cook until all the veggies are cooked through (about another 15 minutes). Remove pan from heat and combine the veggie mixture with the shrimp/pork mixture in bowl and add the other 2 Tablespoons of lime juice. Set this aside & let cool to about room temperature. Once cooled, add the shredded cheese, mix well, & set aside while you make the pupusa dough. Rinse & wipe skillet clean to use again.
In another large bowl, combine the first 6 ingredients for the pupusa dough. Add the water, about a half cup at a time, until the dough forms a large, easy to handle ball. Form the dough into 32 equal sized balls (a little larger than a golf ball), cover with a damp cloth/paper towel & let rest 30 minutes.
Preheat oven to 250`F.
Place 2 pupusa balls about 6" apart between 2 sheets of parchment paper. Press each ball flat using a 6" skillet or plate or whatever you have on hand, to make 2 equal sized rounds. Top one round with 1 - 2 Tablespoons of the filling mixture, then place the other round on top. Press the edges together to enclose the filling and then LIGHTLY press to flatten/even out the thickness of the pupusa, doing your best not to crack the dough or blow out the filling. Perfection is not necessary -- they will still be delicious even if they are "bulging" a little, trust me, we found that out :).
Put your skillet back over medium heat. Brush one side of the filled pupusa with oil and place, oil side down, in skillet. Cook about 2 minutes (until brown spots begin to form), brush the other side of the pupusa with oil, flip and cook another 2 minutes until browned on that side. Place the pupusa on a cookie sheet in oven to keep warm. Continue this process until all the pupusas are done.
Serve these with cilantro, sour cream, lime wedges, and Hidden Valley Original Ranch dressing for dipping!
Note: we had a nice little assembly line going, cooking 2 pupusas at a time in the skillet. Some were brushing with oil and flipping, while others were pressing and forming. Tons O' Fun! FYI, if you have a little filling left over, freeze for later or stuff in some taco shells, super yummy!