Toss together the shrimp and all of the marinade ingredients in a bowl. Cover and chill while you prepare the remaining ingredients, at least 15 minutes.
In the meantime, fry the tortillas. Place a 1/4 inch of oil in a large, sturdy saute pan and heat over medium high heat until shimmering but not smoking. Drop the tortillas in the hot oil and fry until golden and crisp on both sides, about 30 seconds-1 minute on each side. Use tongs to remove the tortillas and place them on a paper towel lined plate to drain. Keep tortillas warm on a sheet pan in a 200 degree oven.
Meanwhile, combine the can of refried beans, cumin, chili powder, and paprika in a small saucepan over medium low heat. Heat until warmed through. Turn the heat off and cover to keep warm.
Drain the oil off the skillet used to fry the tortillas, then heat over medium heat. Cook the marinated shrimp in two batches for about 2 minutes per side, or until no longer pink.
To serve, place the warmed tostada shells on a plate and scoop a few spoonfuls of refried beans onto each of them. Divide the shredded lettuce, tomatoes, jalapeno, avocado, and cilantro evenly over all of them. Sprinkle with salt and a squeeze of fresh lime. Top with the shrimp. Serve immediately.