Make the cottage bean dip: Add the cannellini beans, garlic, lemon juice, lemon zest, olive oil, water, salt, and pepper to a food processor.
Blend until smooth and creamy, scraping down the sides as needed. Add an additional tablespoon of water if you'd like a looser consistency. Taste and adjust seasoning with more salt or lemon juice as desired.
Make the tuna salad: In a medium bowl, combine the tuna, cottage cheese, mayonnaise, capers, red onion, lemon juice, salt, and pepper. Mix until well combined, breaking up the tuna with a fork as you stir. Taste and adjust seasoning with additional lemon juice, salt, or pepper as needed.
Assembly: Toast bread and add the creamy spread, and tuna salad. Add slices of roasted red pepper and artichokes. Top with a big handful of arugula. Close sandwich, slice and enjoy!