If not using a store bought Cajun seasoning then start by preparing the Cajun seasoning by combining all ingredients together in a bowl. Set aside.
Toss the shrimp with one tablespoon olive oil and one-half tablespoon Cajun seasoning. Set aside.
In a large skillet, over medium heat, add the Andouille sausage. Cook, stirring occasionally, until the sausage is browned, approximately 4-5 minutes. Transfer sausage to a plate and set aside.
Add one tablespoon olive oil to the skillet, along with the seasoned shrimp. Spread the shrimp into a single layer in the skillet. Don’t overcrowd them. Cook, stirring once, until the shrimp is opaque and starts to curl. This should take approximately 2 minutes. Do not overcook or your shrimp will have a rubbery texture. Transfer the shrimp to the plate with the sausage.
Add the remaining olive oil to the skillet. Add the onion, garlic, and the diced bell pepper. Sprinkle with additional Cajun seasoning, to taste, and stir to combine. Cook, stirring frequently, until the vegetables soften, approximately4-5 minutes.
Add the yellow squash and zucchini to the skillet. Cook stirring frequently until they are crisp and tender. Remove the skillet from heat and stir in the Andouille sausage, shrimp, salt and pepper to taste and fresh parsley. Stir to combine and serve immediately.