Heat 1 tbsp. oil over high heat in a large frying pan. Add whole sage leaves and fry until crisp, about 30 seconds. Carefully transfer to a paper towel-lined plate (they are quite brittle when fried) and set aside.
Season pork cutlets lightly with salt and pepper and spread one side of each with mustard.
Reduce heat to medium-high and add butter. When foam subsides, add pork, mustard side down, in a single layer and cook, turning once, until golden brown on both sides, about 4 minutes total. Transfer to a clean plate.
Heat remaining 2 tbsp. oil in same pan over medium heat. Add onion and cook until translucent, about 5 minutes. Add garlic and cook 1 minute more. Stir in tomato and cook until it has softened slightly and released some juice, about 3 minutes. Stir in beans, minced sage, zest, 3/4 tsp. salt, and 1/2 tsp. pepper. Reduce heat to low and cook, stirring occasionally, until warm and flavors have melded, about 10 minutes.
To serve, set pork on beans and top with whole sage leaves.
*To butterfly a pork chop, slice it horizontally with a sharp knife almost all the way through, then open it up like a book.