Pat the tenderloin dry with a paper towel. In a small bowl, mix together the coriander, cumin, cinnamon and 3/4 teaspoon salt. Rub the tenderloin with the vegetable oil, then sprinkle with the spice mixture.
Heat a large, oven-safe skillet over medium-high heat. Sear the tenderloin for 3 minutes; flip, and cook an additional 2 minutes. Transfer the skillet to the oven and cook 10 to 15 minutes more, until the tenderloin is medium-rare (125 degrees F on an instant-read thermometer). Remove to a cutting board and let rest 15 minutes.
Combine the mozzarella, mascarpone, ricotta, horseradish, mustard, Worcestershire and smoked paprika in a medium bowl.
Thinly slice the tenderloin. Spread 2 tablespoons of the cheese mixture on each bread slice. Divide the steak and arugula among half the bread slices, then form sandwiches with the remaining bread slices.
Heat the olive oil in a large skillet over medium heat (see Cook's Note). Place the sandwiches in the skillet and weigh them down with a foil-wrapped brick or a heavy lid. Cook for 2 minutes; flip, and cook an additional 2 minutes.
Alternatively, use a panini press, following manufacturer's instructions.