Toss the oxtails and the chicken stock in crockpot on high for 4 hours. Let cool enough to clean the bones and chop the meat, defat and reserve the stock. Chop onion and soften in olive oil. Add lentils, tomatoes and cook per their instruction on package with left over cooking liquid and beef stock. For the last 10 minutes of cooking time add the cauliflower. When lentils are done add in the oxtail meat and serve. Salt and pepper to taste, a dash of lemon juice is good too. I bet a parmesan rind cooking with the lentils would taste great but add calories.