Add the garlic, paprika, oregano, onion powder, salt, pepper, thyme, and cayenne to a small mixing bowl. Stir to combine well. Place in a sealed jar or plastic baggie and store at room temperature until ready to use.
Cajun Ketchup
In a skillet over medium-high heat, warm the olive oil. Add the onion and bell pepper. Cook, stirring a few times until softened, approximately 3 minutes.
Add the diced tomatoes and Cajun seasoning and lower the heat to medium-low. Simmer, stirring often, until the tomatoes have broken down, approximately 6 to 8 minutes.
Remove the pan from the heat and stir in the ketchup. Allow this to cool and transfer to a sealed jar. Refrigerate until ready to use. You can use an immersion blender if you want the ketchup less chunky.
Fries
Slice the potatoes into 1/2-inch thick fries. Alternatively, use a fry cutter to shape the sticks.
Add the potato sticks to a large bowl. Cover with cold water and soak for 30 to 45 minutes to remove excess starch.
Preheat your oven to 425°F. Line a baking sheet with foil or parchment paper.
Drain and rinse the potatoes and pat them very dry with paper towels. Wipe out the bowl so it is dry.
Add the potatoes back to the bowl and coat them with olive oil and Cajun seasoning. Toss to coat well.
Place the potatoes in a single layer on the lined baking sheet. Place this in the preheated oven and bake for 20 minutes. Turn the fries over and continue to bake until browned and crisp, approximately 20 more minutes.
Season the fries with salt, if desired. Serve the hot fries with the Cajun ketchup on the side.