In medium saute pan, heat olive oil over medium-high heat. Sear prawns on both sides until golden brown.
Reduce heat and add white wine to pan to cool. Add piquin pepper and harissa paste and reduce for 2 minutes. Add cold butter and chile flakes. Season the prawns with salt and pepper, to taste. Plate with citrus salad and serve.
Combine the grapefruit segments, orange segments, field greens, shallot, basil, and olive oil in a mixing bowl. Salt and pepper, to taste.