Cajun Salmon and Shrimp

Name: Cajun Salmon and Shrimp
Ingredients: 4 salmon fillets (about 6 oz each); 1/2 lb large shrimp (peeled and deveined); 2 Tbsp Cajun seasoning (store-bought or homemade); 2 Tbsp olive oil; 2 Tbsp butter; 3 cloves garlic (minced); 1/2 cup red onion (minced); 1 Tbsp Flour (optional); 2 cups fresh spinach (roughly chopped); 1 cup heavy cream; 1 cup chicken broth; 1/2 cup grated Parmesan cheese; 1/2 cup shredded mozzarella cheese; 1 tsp Cajun seasoning (optional, for extra heat); Salt and pepper (to taste)