Pat the shrimp completely dry with paper towels and place them in a medium bowl.
Toss the shrimp with the Cajun seasoning, sea salt, and black pepper until evenly coated.
Heat a large skillet over medium-high heat and add 0.5 tablespoon of the grass-fed butter.
Add the sliced bell peppers and red onion to the skillet, sautéing for 3-4 minutes until tender-crisp and slightly charred.
Remove the vegetables from the pan and set aside on a plate.
In the same skillet, add the remaining 1 tablespoon of butter and the minced garlic, stirring for 30 seconds until fragrant.
Add the seasoned shrimp to the pan in a single layer and sear for 2 minutes per side until pink and opaque.
Return the vegetables to the skillet and toss everything together to coat in the garlic butter.
Remove from heat and stir in the fresh lemon juice and chopped parsley before serving.