1. Combine first 4 ingredients in a bowl.
2. Heat oil in a nonstick skillet over medium-high heat. Sprinkle chicken with pepper. Add chicken to pan; cook 5 minutes on each side or until chicken is done. Remove from heat; let stand 5 minutes. Cut lengthwise into 1/3-inch-thick strips. Sprinkle evenly with 1/8 teaspoon salt.
3. Cut baguette in half lengthwise. Spread cheese mixture over cut sides of baguette. Arrange chicken, tomato slices, and arugula evenly over bottom half of baguette; cover with top half. Cut crosswise into 4 equal pieces.
Wine note: Blue cheese's dramatic, salty flavor is the main consideration in matching this sandwich to wine. A crisp, light, dry riesling has the right fruitiness to counteract those salty notes. I love the Penfolds Bin 51 Riesling from Australia's Eden Valley, with its snappy texture. The 2008 is $20. —Karen MacNeil