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 for 15 minutes.
Remove shrimp from marinade, discarding marinade.
Sauté garlic in hot olive oil in a large skillet over medium-high heat for
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.