Using long-handled tongs, moisten a paper towel with cooking oil and lightly coat the grill rack. Brush tuna with olive oil; sprinkle with salt and pepper. Grill, covered, over high heat or broil 3-4 in. from the heat for 2-3 minutes on each side for rare; cook longer if desired. Let stand for 5 minutes. , Meanwhile, in a large bowl, combine the spinach, tomatoes, edamame and corn. In a small bowl, whisk the vinaigrette ingredients; drizzle over salad and toss to coat., Divide salad among four plates; slice tuna and arrange over salads. Serve immediately.