Preheat your oven to 400°.
In a ziplock back, add your cornbread crackers and crush with a rolling pin or meat mallet until only small crumbs remain. Alternatively, you can add them to a food processor and pulse a few times until you reach the desired consistency.
In three bowls, pour crumbs into one, add the beaten egg to another and the flour to the last.
Rinse and pat dry your peeled and deveined shrimp. Coat each one in flour, then egg and lastly cracker crumbs. Place the coated shrimp on a lined baking sheet and spray the breaded shrimp with non-stick spray. Bake at 400° for 8-10 minutes.
Meanwhile, add your cubed avocado, lime juice, garlic, jalapeno, cumin and salt to a bowl and mash until smooth. Fold in your tomatoes and spread each tostada with a generous helping of avocado mixture.
When your shrimp are opaque on the inside and cooked through, remove from the oven and place them on top of the avocado mixture. Garnish the top of the shrimp with finely diced red onion, queso fresco and cilantro. Serve immediately.