In a large skillet over medium heat, heat oil. Add garlic and cook until fragrant, about 1 minute. Add shrimp and squeeze in half the lemon juice. Season with salt and pepper and cook until shrimp are pink, about 2 minutes per side. Transfer to a plate. Deglaze pan with remaining lemon juice. Add chicken broth and linguine and bring to a boil. Cook until most chicken broth is absorbed and pasta al dente, about 10 minutes. Remove from heat and toss in pesto, Parmesan, lemon zest, and cooked shrimp. Top with more Parmesan and red pepper flakes and serve.