Whisk garlic, lemon zest, 1/3 cup parsley, and remaining 6 Tbsp. oil, 1 1/4 tsp. salt, and 1/2 tsp. pepper in a medium bowl until smooth. Transfer half of mixture to another medium bowl. Add panko and Parmesan to first bowl and mix with your hands. Add white beans and tomatoes to second bowl and toss to coat. Whisk mayonnaise and mustard in a small bowl.