Prepare the Cajun seasoning by combining all ingredients together in a bowl. Stir to combine and transfer to an airtight container. Set aside.
Toss the shrimp with one tablespoon olive oil and one-half tablespoon Cajun seasoning. Set aside.
Set a large skillet over medium heat and 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 without overcrowding. Cook,stirring once, just until the shrimp is opaque and starts to curl,approximately 2 minutes. Do not overcook. Transfer shrimp to the plate with the sausage.
Add remaining olive oil to the skillet, along with 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 and develop some color, approximately 4-5 minutes.
Add the yellow squash and zucchini to the skillet and cook, stirring frequently,just until browned and crisp tender, approximately 2-3 minutes. Remove from heat and stir in the Andouille sausage, shrimp, and fresh parsley. Stir to combine and serve immediately.