Preheat the grill or oven to 325°F.

Season the chuck roast generously on all sides with Cajun seasoning and all-purpose seasoning.

Dredge the roast in the 1/3 cup of flour, coating all sides.

Heat the oil in a Dutch oven over medium-high heat.

Once the oil is hot, carefully sear the roast for 3-5 minutes per side, or until nicely browned.

Remove from the heat, but leave the roast in the Dutch oven.

Arrange the sliced onions around the roast.

Add the tomatoes with their juices and 1 cup of beef broth.

Cover and place the Dutch oven on the grill or in the oven.

Cook for approximately 3 hours, or until the roast is fork-tender.

Once the roast is tender, carefully remove it from the Dutch oven and set aside.

Place the Dutch oven over medium heat and bring the tomato mixture to a gentle boil.

In a small bowl, whisk together the remaining 1 cup of beef broth and 2 tablespoons of flour until smooth and free of lumps.

Slowly stir the mixture into the tomatoes to create the gravy.

Continue cooking for about 5 minutes, stirring occasionally, or until the gravy has thickened.

Slice the roast and return it to the gravy.

Serve warm over rice or with biscuits.