Combine first 3 ingredients in a shallow dish; add fish. Cover and chill 20 minutes.
Heat 1 tablespoon vegetable oil in a large nonstick skillet over medium-high heat. Remove fish from marinade, discarding marinade. Add fish to skillet; cook 2 to 3 minutes on each side or to desired degree of doneness. Remove fish; place on a cutting board, and slice into 1/4-inch-thick pieces.
Combine remaining 2 tablespoons vegetable oil, vinegar, and next 3 ingredients in a medium bowl; add salad greens, and toss well. Divide salad evenly between 2 serving plates; top evenly with tuna slices. Serve with Mango Salsa.