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