Heat the oil in a wok or deep-sided skillet on medium-high heat.
Place buttermilk in medium bowl; add shrimp, and soak for 5 minutes.
Place flour and bread crumbs in separate shallow bowls. Drain the shrimp in a sieve over another shallow bowl to capture the buttermilk. Dip the shrimp into flour to coat, then dip in buttermilk, and finally dredge in bread crumbs. Fry the shrimp in hot oil in batches until golden brown, about 3 minutes. Drain on paper towels to absorb any excess oil.
Gently toss the red onion with the orange segments and their juices; add spinach and toss. Drizzle the dressing over the top. Toss to evenly coat the ingredients. Divide salad among 6 large salad pates. Top with shrimp. Season with salt and pepper. Serve immediately.