Cook beef in a large cast-iron skillet over medium heat, stirring often, until browned and crumbly, 6 to 7 minutes. Drain excess fat.
Stir taco seasoning mix, chicken stock, and fire-roasted tomatoes into beef in skillet. Bring to a simmer over medium heat. Reduce heat to medium-low, and cook, uncovered, stirring occasionally, until meat is cooked through, saucy, and liquid clings to beef, 7 to 8 minutes. Remove from heat.
Fluff rice and transfer rice to a serving bowl. Transfer beef mixture to a separate serving bowl. Arrange lettuce, tomatoes, saltine crackers, Cheddar, bell pepper, onion, and sour cream in individual serving bowls.
Assemble individual plates by layering beef mixture over rice and topping as desired.
