1. Combine first 4 ingredients in a large bowl, stirring with a whisk. Add tomatoes; toss gently to coat. Let stand 2 minutes. Arrange tomatoes on a platter so that slices overlap slightly. Reserve remaining vinaigrette in bowl.
2. Add arugula, cucumber, onion, mint, and falafel to reserved vinaigrette in bowl; toss gently to coat. Arrange falafel mixture over tomatoes; sprinkle evenly with feta and pine nuts. Drizzle any remaining vinaigrette over salad.