In a medium skillet, heat 3 tablespoons olive oil over medium-high heat. Add the shrimp and stir-fry until opaque, 2 to 3 minutes.
In a medium bowl, whisk together the shallot, vinegar, mustard and honey; season with salt and pepper. Pour in the remaining 1/4 cup olive oil in a slow stream, whisking constantly until thick. Using a slotted spoon, transfer the cooked shrimp to the dressing and toss to coat. Season to taste with salt and pepper.
Arrange the spinach on a platter or individual plates. Place the warm shrimp on top and drizzle with any remaining dressing. Scatter the feta on top.