In a medium bowl, toss together the shrimp with the Chinese five-spice powder until evenly coated. Add the orange juice, orange zest, soy sauce, vegetable oil, garlic, red pepper flakes, and 1 teaspoon salt and toss to combine. Cover and refrigerate the shrimp for a minimum of 30 minutes and up to 2 hours, if time allows.
Heat a large saute pan over medium-high heat. Add the shrimp in batches and cook them in a single layer until they are cooked through, about 1 minute on each side. Transfer the shrimp to a serving plate.
In a small bowl, whisk together the sour cream and lime juice with 1/2 teaspoon salt.
Drizzle the shrimp with the sauce and serve with tortillas, sliced radishes and diced avocado.