In a food processor bowl or blender container combine arugula, oil, lemon juice, garlic, and salt. Cover and process or blend until nearly smooth. Add cannellini beans. Cover and process or blend just until coarsely chopped and mixture is combined (mixture should be slightly chunky). Transfer bean mixture to a serving bowl. Gently stir in chopped tomato. Serve immediately or cover and chill up to 24 hours. Serve with crackers, baguette slices, or vegetable dippers. Makes about 1-1/2 cups dip.