Boil water with chicken bouillon paste if using. Cook pasta until al dente, reserve 1 1/2 cups pasta water, then drain.
Season shrimp with 1 1/2 tsp cajun seasoning, salt, and pepper.
Heat olive oil in large skillet over medium heat. Brown sausage 5-7 minutes, remove to bowl.
Cook shrimp in same pan 2-3 minutes until pink and curled, add to bowl with sausage.
Add onion, bell peppers, and celery to pan. Cook 5-7 minutes until softened.
Add garlic and cook 2 minutes until fragrant.
Stir in tomato paste, garlic powder, onion powder, and remaining cajun seasoning. Cook 3-4 minutes, stirring constantly.
Pour in chicken broth and diced tomatoes, scraping up browned bits.
Add heavy cream, reduce heat to low, and simmer 5-7 minutes until thickened.
Stir in spinach, parmesan, and lemon juice until spinach wilts.
Add 3/4 cup reserved pasta water and stir until creamy.
Add pasta to sauce and toss to coat.
Top with shrimp, sausage, and fresh parsley. Serve immediately.