Roasted Shrimp Tostadas with Avocado-Yogurt Sauce

Oh, what a delight this dish is!  It's also quick and easy.  Once you start eating, you won't want to stop.  The avocado-yogurt sauce is absolutely amazing and it goes perfectly with the roasted shrimp.  Enjoy!
For avocado-yogurt sauce:
-2 medium ripe avocados, peeled and seeded
-1/2 cup plain nonfat Greek yogurt
-2 tsp lemon juice
-1 tsp garlic powder
-1/2 tsp salt
For tostadas:
-8 corn tortillas
-extra virgin olive oil
-12 oz medium shrimp, peeled, deveined, with tails removed
-1 tsp chili powder
-1 tsp cumin
-shredded lettuce, for topping
-shredded cheese (either cheddar or mozzarella work just fine), for topping
-green onions, chopped, for topping
-tomatoes, chopped, for topping
Preheat oven to 400 F.
Make the sauce by adding all of the ingredients into your food processor.  Process until smooth and creamy.  Pour into serving bowl and set aside.
Brush each corn tortilla with the olive oil on both sides.  Place on baking sheet and pop in the hot oven.  Bake for about 5 minutes on each side or until lightly browned and crisp.  
Place shrimp on another baking sheet.  Sprinkle with the chili powder and cumin.  Using your hands, mix well, then spread into single layer.  Roast in preheated oven for 10 minutes.
To assemble, place one crisp tortilla on your plate.  Top with lettuce, cheese, 3-4 shrimp, sauce, onions and tomatoes.  Enjoy!