Season the chicken. In a medium mixing bowl toss together the diced chicken with 1 tablespoon of Cajun seasoning, until evenly coated.
Cook the chicken. Heat 2 tablespoons of the oil in a large Dutch oven or wide-bottomed (and preferably deep) pot over medium-high heat. Add the chicken and saute until lightly golden and cooked through. Remove the chicken to a plate.
Cook the sausage. Add the remaining 1 tablespoon of oil along with the sausage to the same pan and saute for a couple of minutes, until lightly browned on both sides. Remove the sausage to the plate with the chicken.
Saute the veggies. Add the onion, bell pepper, and celery, and saute for 4 to 5 minutes, until the veggies have softened. If you need to add a splash more oil feel free to do so.
Add the garlic and spices. Add the minced garlic, the remaining 1 tablespoon of Cajun seasoning, and the red pepper flakes to the pan. Stir together for 30 seconds.
Add the rice and liquid. Add the rice and toast with the veggies and spices by stirring for a minute. Then add the bay leaf, tomatoes, and broth. Give it a stir, bring to a simmer, then reduce the heat to low, and cover. Cook for about 7 to 8 minutes, stirring occasionally just to make sure the rice isn't sticking to the bottom of the pot, until the rice is al dente. *see notes on rice below
Add the shrimp. Remove the bay leaf, add the shrimp to the pan along with the sausage and chicken, gently stir, cover, and turn off the heat. The shrimp will cook through in about 4 to 5 minutes, and all of the liquid should be absorbed by the rice. Taste the jambalaya and season with extra salt and pepper if you'd like.
Garnish. Before serving, garnish with sliced green onions and chopped parsley.