Add the minced garlic to a small bowl, and mash it into a paste.
Add the lemon zest and juice, and Dijon mustard. Whisk together until thoroughly blended. Add 1/4 teaspoon salt, and 1/2 teaspoon pepper, and continue to stir.
Reserve about 1 1/2 tablespoons olive oil and set aside. Add the rest little by little to the lemon/mustard/garlic mixture, stirring with a whisk as you do. The dressing should thicken.
Add 1 tablespoon of oil to a skillet and heat over a medium-high setting. Add the French bread cubes and sprinkle with about 1/8 teaspoon salt. Cook and stir until golden brown and crunchy, about 4 to 6 minutes. Set aside.
Brush the chicken breast halves with the remaining 1/2 tablespoon oil and sprinkle with remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper. Place on a broiler rack about 4-5-inches from the heat for about 12 to 15 minutes, turning once halfway through.
Once the chicken is thoroughly cooked, remove from the broiler and allow it to cool about 5 to 10 minutes. Slice crosswise into about 1/4-inch slices.
Place the romaine lettuce into a large bowl. Drizzle with the dressing and toss to coat. Sprinkle with cheese, and toss again to distribute evenly.
Divide the salad into four and distribute onto plates. Top each with a quarter of the croutons and a quarter of the cooked chicken slices.