Finely chop the large onion, green and red bell peppers, celery stalks, garlic cloves, and parsley leaves. Pat the boneless chicken thighs dry and season them generously with Cajun seasoning. Set everything aside in organized bowls for easy access during cooking.

In a large skillet, heat avocado oil over medium-high heat. Add the seasoned chicken thighs and sear them for 3-5 minutes on each side until golden brown. Remove from skillet and set aside.

Lower the heat to medium, melt unsalted butter in the same skillet, and whisk in all-purpose flour, stirring continuously for 10-15 minutes until a medium brown color is achieved.

Add the chopped onion, green bell pepper, and red bell pepper to the skillet, sauté for about 10 minutes. Stir in minced garlic and cook for an additional minute.

Gradually whisk in warm chicken broth ensuring a smooth mixture. Add browning sauce, return seared chicken to skillet, and simmer for about 30 minutes.

Remove skillet from heat, chop chicken into bite-sized pieces, return to pot, stir in chopped parsley, and adjust seasoning if needed.

Serve Chicken Étouffée over warm cooked white rice and garnish with chopped green onions.