In a small saucepan, heat olive oil over medium heat. Add rosemary, thyme, oregano, and garlic powder; cook for 3 minutes. Add flour; cook, stirring constantly, for 2 minutes. Gradually add chicken broth, whisking until smooth. Add lemon juice, salt, and pepper. Bring to a simmer; cook for 20 minutes, stirring occasionally, until sauce is slightly thickened.