Place shrimp in a gallon sized resealable bag.
In a small bowl, whisk together olive oil, garlic, soy sauce, honey, balsamic vinegar and pepper. Reserve one cup and set aside.
Pour remaining marinade over shrimp, seal bag and refrigerate for 1 hour.
Heat a large nonstick skillet over high heat and spray with cooking spray. Sear shrimp for 1 minute on each side, or until edges start to brown.
Pour reserved cup of marinade into a small saucepan over medium-high heat. In a small bowl, whisk water and cornstarch, then whisk mixture into marinade.
Bring to a simmer, stirring continuously, until thickened. Gently toss shrimp in sauce and serve.