In a small bowl, combine 2 tablespoons avocado, water, 1 teaspoon lime juice, 1 teaspoon blackened seasoning and cumin. Set aside 1/4 cup beans; add remaining beans to avocado mixture and mash with a fork. Stir in reserved beans. Set aside.
For salsa, in a small bowl, combine the orange, onion, jalapeno, cilantro and remaining avocado and lime juice. Cover and refrigerate until serving.
Place tostada shells on ungreased baking sheets; spread with bean mixture. Sprinkle with cheese. Bake at 350° for 4-6 minutes or until cheese is melted.
Meanwhile, in a large nonstick skillet coated with cooking spray, cook shrimp and remaining blackened seasoning over medium-high heat for 4-6 minutes or until shrimp turn pink. Arrange over tostada shells; serve with salsa.