Preheat oven to 200°C/ gas mark 7.
For the dressing, blend all the ingredients except the olive oil until smooth. While machine is running, slowly drizzle in the oil until incorporated. Season, to taste, with salt and pepper.
Grease a 20 by 20cm glass pan with butter. Stir together the cornbread mix with the egg and milk. Evenly spread into prepared pan and bake on the middle rack for 20 minutes. Remove from oven and cool in pan for ten minutes. Remove from pan to cool completely.
Mix together the beans with the sazon and season with salt and pepper. Toss the salsa with the tomatoes. When ready to serve, cut the cornbread into 1cm croutons.
Toss the lettuce with 190ml of the dressing. In a clear trifle dish, layer the Tex-Mex Salad beginning with the black beans followed by the Monterey jack cheese, the tomato salsa mixture, the Cheddar, the dressed romaine and top with the cornbread croutons. Serve the remaining dressing on the side.