In a food processor blend the Saladitas crackers to make a fine crumb.
Heat oil to 350 °F in a heavy deep pot or fryer.
To clean shrimp, remove the shell and slice into the shrimp with a pairing knife and scrape out the vein; make a deeper cut for butterflying the shrimp.
In a large bowl mix 1 cup of all-purpose flour, mustard, garlic powder, black pepper, oregano, cumin, and light beer; whisk together to make the batter. Do not over mix.
Lightly dredge the shrimp in the remaining flour. Pick up the shrimp by their tails and dip the bodies in the batter and coat with the Saladitas crackers crumbs. Immediately deep fry until crisp and light golden brown.
Drain the shrimp on paper towels and serve immediately.