1. Preheat grill to medium-high heat.
2. Brush pork with oil. Place pork on a grill rack coated with cooking spray; grill 6 minutes on each side or until a thermometer inserted into thickest portion of pork registers 145°. Remove from grill; let pork stand 5 minutes. Slice pork crosswise in half; slice each half, lengthwise, into thin strips. Cool. Combine juice and next 6 ingredients (through serrano) in a large bowl. Add pork to juice mixture; toss to coat. Add mint and next 3 ingredients (through cucumber) to bowl; toss. Arrange 2 cups lettuce on each of 4 plates; top each serving with about 2/3 cup pork mixture. Sprinkle with cilantro.