Add the remaining 2 teaspoons oil and garlic to the pan and cook, stirring, until fragrant, about 30 seconds. Add shrimp and cook, stirring, for 1 minute. Whisk broth and cornstarch in a small bowl until smooth and add to the pan along with the remaining ¼ teaspoon salt. Cook, stirring, until the sauce has thickened slightly and the shrimp are pink and just cooked through, about 2 minutes more. Remove from the heat. Stir in lemon juice and parsley. Serve the shrimp and sauce over the vegetables.