Prepare the Honey-Lime Cilantro Dressing:

In a small bowl, whisk together the lime juice, lemon juice, honey, and oil until well combined. Stir in the cilantro. Season with salt and pepper to taste.

Prepare the salad:

Season the tuna with salt and pepper. In a large skillet over medium-high heat, warm the oil until a few water droplets sizzle in the pan. Quickly sear the tuna, leaving the tuna rare inside, until well browned and easily releases from the pan, about 2 minutes per side. Transfer to a cutting board and slice thinly.

In a large salad bowl, toss the spring lettuce mix with the mango and red onion. Add the dressing to taste, reserving some to drizzle on top of the fish, and gently toss. Season with salt and pepper to taste.

Divide the salad equally among individual plates. Place the sliced tuna next to the salad. Drizzle the reserved dressing over the tuna. Serve immediately.