Whisk together sour cream, 1 teaspoon chili powder, 1/2 teaspoon cumin, 1/2 teaspoon red pepper, 1/4 teaspoon salt, and cinnamon. Add 1 1/2 cups water, stirring until smooth. Cover and chill until ready to serve.
Peel shrimp, and devein, if desired; chop. Combine remaining 1 teaspoon chili powder, 1/2 teaspoon cumin, 1/4 teaspoon red pepper, and 1/2 teaspoon salt in a shallow dish or heavy-duty zip-top plastic bag; add orange juice and shrimp, turning to coat. Cover or seal, and chill 15 minutes. Remove shrimp from marinade, discarding marinade.
Sauté garlic in hot olive oil in a large skillet over medium-high heat 2 to 3 minutes. Add shrimp, and cook 5 minutes or just until shrimp turn pink. Serve with sour cream mixture and avocado in warm tortillas.