1) In a large dish, mix 3 tbsp. maple syrup, 2 tbsp. olive oil, 1 tbsp. lemon juice, 1 1/2 tbsp. Dijon mustard, 1/4 tsp. salt, 1/4 tsp. pepper together. Reserve about four tablespoons of the marinade. Add 2 - 5oz tuna steaks to the dish, and turn them until they’re well-coated. Set aside, and let them rest at room temperature for about 20-30 minutes. 2) Heat up a non-stick skillet over high heat. Sear the tuna steaks for about 1-3 minutes on each side, or until the steaks reach their desired doneness. Place the cooked steaks on a cutting board, and slice against the grain into ½-inch thick slices. Transfer the steak slices to a serving plate and drizzle with the reserved maple-mustard marinade. Serve immediately.