Strain tomatoes in a colander over a bowl, reserving ¼ cup liquid. Add strained tomato mixture, ¼ cup reserved tomato liquid, Cajun seasoning, salt, and rice to pan, scraping pan with a wooden spoon to loosen browned bits. Cover pan, reduce heat to medium, and simmer 10 minutes, stirring occasionally. Remove pan from heat; sprinkle with green onions. Divide rice mixture evenly among 4 bowls. Serve with lemon wedges and hot sauce, if desired.