Stem jalapeño peppers, halve, seed, and mince. For more heat, leave some or all seeds in. Halve grape tomatoes. Cut butcher’s twine into four 9” lengths. Pat pork tenderloin dry.

Lay pork on a separate cutting board. Hold knife blade parallel to board and carefully make a lengthwise cut through center of pork, using your free hand to steady pork. Stop short of opposite edge of tenderloin so pork remains in one piece and opens like a book. Cover with plastic wrap. Using an heavy object like a small pot, pound to an even 1/3" thickness. Season both sides with 1/2 tsp. salt and 1/4 tsp. pepper.

Combine cream cheese, cheddar cheese, 2 Tbsp. warm water, and jalapeños (to taste) in a small mixing bowl. Mixture should be easily spreadable, like peanut butter. If too thick, add water 1 Tbsp. at a time to reach correct consistency. Spread evenly on butterflied pork, leaving a 1" border. Roll tenderloin lengthwise, completely enclosing stuffing. Tie pork shut, spacing four knots of butcher's twine across the length of the tenderloin.

Heat 2 tsp. olive oil in a medium non-stick pan over medium heat. Add tenderloin to hot pan, bending to fit if necessary. Cook until golden brown on three sides, 8-10 minutes. Transfer to baking sheet and roast until tenderloin reaches a minimum internal temperature of 145 degrees, 20-25 minutes. Rest 5 minutes. Wipe pan clean and place over medium-high heat. Add evaporated milk and half the ranch seasoning to hot pan. Bring to a simmer and cook until slightly thickened, 1 minute. Taste, and add remaining ranch seasoning if desired.

Place seasoned rice vinegar, 11/2 Tbsp. olive oil, red cabbage, tomatoes, and arugula in a medium mixing bowl. Toss to combine and season to taste with salt and pepper.

Cut twine from pork and slice into 3/4"-1" rounds. Spoon sauce onto plate, place salad next to sauce, and arrange sliced pork on sauce.