Combine 2 tablespoons vinegar, 1 tablespoon honey, ⅛ teaspoon salt and smashed garlic in a medium bowl; whisk well.
Heat 2 teaspoons oil in a medium nonstick skillet over medium heat. Add trimmed chicken thighs; cook, flipping once, until an instant-read thermometer inserted into the thickest part of the chicken registers 165°F, 10 to 12 minutes. Reduce heat to medium-low; add the balsamic mixture and continue cooking, turning and basting the chicken with the sauce, until the sauce is bubbling and thickened, about 2 minutes more.
Combine 2 cups arugula, the chopped tomato, 1 teaspoon lemon juice, ⅛ teaspoon pepper and the remaining 2 teaspoons oil and ⅛ teaspoon salt in a medium bowl; toss to combine. Serve the salad with the chicken. Drizzle any remaining sauce over the chicken.
