Ingredients

• 2 tablespoons cooking oil, divided

• 3 tablespoons butter, divided

• 4 boneless, skinless chicken breasts (about 1 1/3 pounds total)

• 1 teaspoon kosher salt, divided

• 1/2 teaspoon freshly ground black pepper, divided

• 1/2 red onion, chopped

• 2 garlic cloves, chopped

• 3/4 pound fresh brussels sprouts (or 1 [10-ounce] package frozen), cut into quarters from top to stem end

• 1 cup canned low-sodium chicken broth or homemade stock

• 1/8 teaspoon dried red pepper flakes

• 1 1/2 teaspoons lemon juice

• 1/4 cup chopped fresh parsley

• 1/3 cup grated Parmesan cheese

• 1/2 pound medium pasta shells