Stir in the garlic and Cajun seasoning. Cook for about 30 seconds, just until the garlic is fragrant and the spices bloom.
Add the rice and toast it with the vegetables for 1–2 minutes, so the grains look lightly opaque at the edges and glossy with oil.
Pour in the chicken broth and crushed tomatoes (if using). Bring to a gentle boil, then reduce the heat to a simmer. Cover and cook 18–20 minutes, or until the rice is tender and most of the liquid is absorbed. If needed, cook a few minutes more, but avoid overcooking.
Place the shrimp on top of the rice in a single layer. Re-cover and cook 3–4 minutes, until the shrimp are pink, opaque, and just cooked through. They should curl slightly and look glossy.
Remove from heat. Fluff the rice with a fork, fold in the parsley, and taste for salt and pepper. If you like it hotter, splash with hot sauce, or squeeze a little lemon for brightness. Let it rest 2 minutes before serving.
